path: root/xc/programs/Xserver/hw/xfree86/doc/DESIGN

                   XFree86 X server ``New Design'' (DRAFT)

                          The XFree86 Project, Inc

                       Last modified 25 November 1999

NOTE: This is a DRAFT document, and the interfaces described here are subject
to change without notice.

1.  Preface

The broad design principles are:

   o keep it reasonable

        o We cannot rewrite the complete server

        o We don't want to re-invent the wheel

   o keep it modular

        o As many things as possible should go into modules

        o The basic loader binary should be minimal

        o A clean design with well defined layering is important

        o DDX specific global variables are a nono

        o The structure should be flexible enough to allow future extensions

        o  The structure should minimize duplication of common code

   o keep important features in mind

        o multiple screens, including multiple instances of drivers

        o mixing different color depths and visuals on different and ideally
          even on the same screen

        o better control of the PCI device used

        o better config file parser

        o get rid of all VGA compatibility assumptions

Unless we find major deficiencies in the DIX layer, we should avoid making
changes there.

2.  The XF86Config File

The XF86Config file format is similar to the old format, with the following
changes:

2.1  Device section

The Device sections are similar to what they used to be, and describe hard-
ware-specific information for a single video card.  Device Some new keywords
are added:

      Driver "drivername"
            Specifies the name of the driver to be used for the card.  This
            is mandatory.

      BusID "busslot"
            Specifies uniquely the location of the card on the bus.  The pur-
            pose is to identify particular cards in a multi-headed configura-
            tion.  The format of the argument is intentionally vague, and may
            be architecture dependent.  For a PCI bus, it is something like
            "bus:slot:func".

A Device section is considered ``active'' if there is a reference to it in an
active Screen section.

2.2  Screen section

The Screen sections are similar to what they used to be.  They no longer have
a Driver keyword, but an Identifier keyword is added.  (The Driver keyword
may be accepted in place of the Identifier keyword for compatibility pur-
poses.)  The identifier can be used to identify which screen is to be active
when multiple Screen sections are present.  It is possible to specify the
active screen from the command line.  A default is chosen in the absence of
one being specified.  A Screen section is considered ``active'' if there is a
reference to it either from the command line, or from an active ServerLayout
section.

2.3  InputDevice section

The InputDevice section is a new section that describes configuration infor-
mation for input devices.  It replaces the old Keyboard, Pointer and XInput
sections.  Like the Device section, it has two mandatory keywords: Identifier
and Driver.  For compatibility purposes the old Keyboard and Pointer sections
are converted by the parser into InputDevice sections as follows:

      Keyboard
            Identifier "Implicit Core Keyboard"

            Driver "keyboard"

      Pointer
            Identifier "Implicit Core Pointer"

            Driver "mouse"

An InputDevice section is considered active if there is a reference to it in
an active ServerLayout section.  An InputDevice section may also be refer-
enced implicitly if there is no ServerLayout section, if the -screen command
line options is used, or if the ServerLayout section doesn't reference any
InputDevice sections.  In this case, the first sections with drivers "key-
board" and "mouse" are used as the core keyboard and pointer respectively.

2.4  ServerLayout section

The ServerLayout section is a new section that is used to identify which
Screen sections are to be used in a multi-headed configuration, and the rela-
tive layout of those screens.  It also identifies which InputDevice sections
are to be used.  Each ServerLayout section has an identifier, a list of
Screen section identifiers, and a list of InputDevice section identifiers.
ServerFlags options may also be included in a ServerLayout section, making it
possible to override the global values in the ServerFlags section.

A ServerLayout section can be made active by being referenced on the command
line.  In the absence of this, a default will be chosen (the first one
found).  The screen names may optionally be followed by a number specifying
the preferred screen number, and optionally by information specifying the
physical positioning of the screen, either in absolute terms or relative to
another screen (or screens).  When no screen number is specified, they are
numbered according to the order in which they are listed.  The old (now obso-
lete) method of providing the positioning information is to give the names of
the four adjacent screens.  The order of these is top, bottom, left, right.
Here is an example of a ServerLayout section for two screens using the old
method, with the second located to the right of the first:

           Section "ServerLayout"
             Identifier "Main Layout"
             Screen     "Screen 1" 0 ""  ""  ""  "Screen 2"
             Screen     "Screen 2" 1
             Screen     "Screen 3"
           EndSection

The preferred way of specifying the layout is to explicitly specify the
screen's location in absolute terms or relative to another screen.

In the absolute case, the upper left corner's coordinates are given after the
Absolute keyword.  If the coordinates are omitted, a value of (0,0) is
assumed.  An example of absolute positioning follows:

           Section "ServerLayout"
             Identifier "Main Layout"
             Screen     "Screen 1" 0 Absolute 0 0
             Screen     "Screen 2" 1 Absolute 1024 0
             Screen     "Screen 3" Absolute 2048 0
           EndSection

In the relative case, the position is specified by either using one of the
following keywords followed by the name of the reference screen:

     RightOf

     LeftOf

     Above

     Below

     Relative

When the Relative keyword is used, the reference screen name is followed by
the coordinates of the new screen's origin relative to reference screen.  The
following example shows how to use some of the relative positioning options.

           Section "ServerLayout"
             Identifier "Main Layout"
             Screen     "Screen 1" 0
             Screen     "Screen 2" 1 RightOf "Screen 1"
             Screen     "Screen 3" Relative "Screen 1" 2048 0
           EndSection

2.5  Options

Options are used more extensively.  They may appear in most sections now.
Options related to drivers can be present in the Screen, Device and Monitor
sections and the Display subsections.  The order of precedence is Display,
Screen, Monitor, Device.  Options have been extended to allow an optional
value to be specified in addition to the option name.  For more details about
options, see the Options (section 10., page 1) section for details.

3.  Driver Interface

The driver interface consists of a minimal set of entry points that are
required based on the external events that the driver must react to.  No non-
essential structure is imposed on the way they are used beyond that.  This is
a significant difference compared with the old design.

The entry points for drawing operations are already taken care of by the
framebuffer code (including, XAA).  Extensions and enhancements to frame-
buffer code are outside the scope of this document.

This approach to the driver interface provides good flexibility, but does
increase the complexity of drivers.  To help address this, the XFree86 common
layer provides a set of ``helper'' functions to take care of things that most
drivers need.  These helpers help minimise the amount of code duplication
between drivers.  The use of helper functions by drivers is however optional,
though encouraged.  The basic philosophy behind the helper functions is that
they should be useful to many drivers, that they should balance this against
the complexity of their interface.  It is inevitable that some drivers may
find some helpers unsuitable and need to provide their own code.

Events that a driver needs to react to are:

      ScreenInit
            An initialisation function is called from the DIX layer for each
            screen at the start of each server generation.

      Enter VT
            The server takes control of the console.

      Leave VT
            The server releases control of the console.

      Mode Switch
            Change video mode.

      ViewPort change
            Change the origin of the physical view port.

      ScreenSaver state change
            Screen saver activation/deactivation.

      CloseScreen
            A close screen function is called from the DIX layer for each
            screen at the end of each server generation.

In addition to these events, the following functions are required by the
XFree86 common layer:

      Identify
            Print a driver identifying message.

      Probe
            This is how a driver identifies if there is any hardware present
            that it knows how to drive.

      PreInit
            Process information from the XF86Config file, determine the full
            characteristics of the hardware, and determine if a valid config-
            uration is present.

The VidMode extension also requires:

      ValidMode
            Identify if a new mode is usable with the current configuration.
            The PreInit function (and/or helpers it calls) may also make use
            of the ValidMode function or something similar.

Other extensions may require other entry points.  The drivers will inform the
common layer of these in such cases.

4.  Resource Access Control Introduction

Graphics devices are accessed through ranges in I/O or memory space.  While
most modern graphics devices allow relocation of such ranges many of them
still require the use of well established interfaces such as VGA memory and
IO ranges or 8514/A IO ranges.  With modern buses (like PCI) it is possible
for multiple video devices to share access to these resources.  The RAC
(Resource Access Control) subsystem provides a mechanism for this.

4.1  Terms and Definitions

4.1.1  Bus

``Bus'' is ambiguous as it is used for different things: it may refer to
physical incompatible extension connectors in a computer system.  The RAC
system knows two such systems: The ISA bus and the PCI bus.  (On the software
level EISA, MCA and VL buses are currently treated like ISA buses).  ``Bus''
may also refer to logically different entities on a single bus system which
are connected via bridges.  A PCI system may have several distinct PCI buses
connecting each other by PCI-PCI bridges or to the host CPU by HOST-PCI
bridges.

Systems that host more than one bus system link these together using bridges.
Bridges are a concern to RAC as they might block or pass specific resources.
PCI-PCI bridges may be set up to pass VGA resources to the secondary bus.
PCI-ISA buses pass any resources not decoded on the primary PCI bus to the
ISA bus.  This way VGA resources (although exclusive on the ISA bus) can be
shared by ISA and PCI cards.  Currently HOST-PCI bridges are not yet handled
by RAC as they require specific drivers.

4.1.2  Entity

The smallest independently addressable unit on a system bus is referred to as
an entity.  So far we know ISA and PCI entities.  PCI entities can be located
on the PCI bus by an unique ID consisting of the bus, card and function num-
ber.

4.1.3  Resource

``Resource'' refers to a range of memory or I/O addresses an entity can
decode.

If a device is capable of disabling this decoding the resource is called
sharable.  For PCI devices a generic method is provided to control resource
decoding.  Other devices will have to provide a device specific function to
control decoding.

If the entity is capable of decoding this range at a different location this
resource is considered relocatable.

Resources which start at a specific address and occupy a single continuous
range are called block resources.

Alternatively resource addresses can be decoded in a way that they satisfy
the conditions:

                              address & mask == base

and

                                 base & mask == base

Resources addressed in such a way are called sparse resources.

4.1.4  Server States

The resource access control system knows two server states: the SETUP and the
OPERATING state.  The SETUP state is entered whenever a mode change takes
place or the server exits or does VT switching.  During this state all entity
resources are under resource access control.  During OPERATING state only
those entities are controlled which actually have shared resources that con-
flict with others.

5.  Control Flow in the Server and Mandatory Driver Functions

At the start of each server generation, main() (dix/main.c) calls the DDX
function InitOutput().  This is the first place that the DDX gets control.
InitOutput() is expected to fill in the global screenInfo struct, and one
screenInfo.screen[] entry for each screen present.  Here is what InitOutput()
does:

5.1  Parse the XF86Config file

This is done at the start of the first server generation only.

The XF86Config file is read in full, and the resulting information stored in
data structures.  None of the parsed information is processed at this point.
The parser data structures are opaque to the video drivers and to most of the
common layer code.

The entire file is parsed first to remove any section ordering requirements.

5.2  Initial processing of parsed information and command line options

This is done at the start of the first server generation only.

The initial processing is to determine paths like the ModulePath, etc, and to
determine which ServerLayout, Screen and Device sections are active.

5.3  Enable port I/O access

Port I/O access is controlled from the XFree86 common layer, and is ``all or
nothing''.  It is enabled prior to calling driver probes, at the start of
subsequent server generations, and when VT switching back to the Xserver.  It
is disabled at the end of server generations, and when VT switching away from
the Xserver.

The implementation details of this may vary on different platforms.

5.4  General bus probe

This is done at the start of the first server generation only.

In the case of ix86 machines, this will be a general PCI probe.  The full
information obtained here will be available to the drivers.  This information
persists for the life of the Xserver.  In the PCI case, the PCI information
for all video cards found is available by calling xf86GetPciVideoInfo().

     pciVideoPtr *xf86GetPciVideoInfo(void)

          returns a pointer to a list of pointers to pciVideoRec
          entries, of which there is one for each detected PCI
          video card.  The list is terminated with a NULL pointer.
          If no PCI video cards were detected, the return value is
          NULL.

After the bus probe, the resource broker is initialised.

5.5  Load initial set of modules

This is done at the start of the first server generation only.

The core server contains a list of mandatory modules.  These are loaded
first.  Currently the only module on this list is the bitmap font module.

The next set of modules loaded are those specified explicitly in the Module
section of the config file.

The final set of initial modules are the driver modules referenced by the
active Device and InputDevice sections in the config file.  Each of these
modules is loaded exactly once.

5.6  Register Video and Input Drivers

This is done at the start of the first server generation only.

When a driver module is loaded, the loader calls its Setup function.  For
video drivers, this function calls xf86AddDriver() to register the driver's
DriverRec, which contains a small set of essential details and driver entry
points required during the early phase of InitOutput().  xf86AddDriver() adds
it to the global xf86DriverList[] array.

The DriverRec contains the driver's version, a short descriptive message, the
Identify() and Probe() function entry points as well as a pointer to the
driver's module (as returned from the loader when the driver was loaded) and
a reference count which keeps track of how many screens are using the driver.
The entry driver entry points are those required prior to the driver allocat-
ing and filling in its ScrnInfoRec.

For a static server, the xf86DriverList[] array is initialised at build time,
and the loading of modules is not done.

A similar procedure is used for input drivers.  The input driver's Setup
function calls xf86AddInputDriver() to register the driver's InputDriverRec,
which contains a small set of essential details and driver entry points
required during the early phase of InitInput().  xf86AddInputDriver() adds it
to the global xf86InputDriverList[] array.  For a static server, the
xf86InputDriverList[] array is initialised at build time.

Both the xf86DriverList[] and xf86InputDriverList[] arrays have been ini-
tialised by the end of this stage.

Once all the drivers are registered, their ChipIdentify() functions are
called.

     void ChipIdentify(int flags)

          This is expected to print a message indicating the driver
          name, a short summary of what it supports, and a list of
          the chipset names that it supports.  It may use the
          xf86PrintChipsets() helper to do this.

     void xf86PrintChipsets(const char *drvname, const char *drvmsg,

               SymTabPtr chips)

          This function provides an easy way for a driver's ChipI-
          dentify function to format the identification message.

5.7  Initialise Access Control

This is done at the start of the first server generation only.

The Resource Access Control (RAC) subsystem is initialised before calling any
driver functions that may access hardware.  All generic bus information is
probed and saved (for restoration later).  All (shared resource) video
devices are disabled at the generic bus level, and a probe is done to find
the ``primary'' video device.  These devices remain disabled for the next
step.

5.8  Video Driver Probe

This is done at the start of the first server generation only.  The Chip-
Probe() function of each registered video driver is called.

     Bool ChipProbe(DriverPtr drv, int flags)

          The purpose of this is to identify all instances of hard-
          ware supported by the driver.  The flags value is cur-
          rently not used, and should be ignored by the driver.

          The probe must find the active device sections that match
          the driver by calling xf86MatchDevice().  The number of
          matches found limits the maximum number of instances for
          this driver.  If no matches are found, the problem should
          return FALSE immediately.

          Devices that cannot be identified by using device-inde-
          pendent methods should be probed at this stage (keeping
          in mind that access to all resources that can be disabled
          in a device-independent way are disabled during this
          phase).  The probe must be a minimal probe.  It should
          just determine if there is a card present that the driver
          can drive.  It should use the least intrusive probe meth-
          ods possible.  It must not do anything that is not essen-
          tial, like probing for other details such as the amount
          of memory installed, etc.  It is recommended that the
          xf86MatchPciInstances() helper function be used for iden-
          tifying matching PCI devices, and similarly the
          xf86MatchIsaInstances() for ISA (non-PCI) devices (see
          the RAC (section 9., page 1) section).  These helpers
          also checks and claims the appropriate entity.  When not
          using the helper, that should be done with xf86CheckPciS-
          lot() and xf86ClaimPciSlot() for PCI devices and
          xf86ClaimIsaSlot() for ISA devices (see the RAC (section
          9., page 1) section).

          The probe must register all non-relocatable resources at
          this stage.  If a resource conflict is found between
          exclusive resources the driver will fail immediately.
          This is usually best done with the xf86ConfigActivePciEn-
          tity() helper function for PCI and xf86ConfigActiveIsaEn-
          tity() for ISA (see the RAC (section 9., page 1) sec-
          tion).  It is possible to register some entity specific
          functions with those helpers.  When not using the
          helpers, the xf86AddEntityToScreen() xf86ClaimFixe-
          dResources() and xf86SetEntityFuncs() should be used
          instead (see the RAC (section 9., page 1) section).

          If a chipset is specified in an active device section
          which the driver considers relevant (ie it has no driver
          specified, or the driver specified matches the driver
          doing the probe), the Probe must return FALSE if the
          chipset doesn't match one supported by the driver.

          If there are no active device sections that the driver
          considers relevant, it must return FALSE.

          Allocate a ScrnInfoRec for each instance of the hardware
          found, and fill in the basic information, including the
          other driver entry points.  The xf86AllocateScreen()
          function must be used to allocate the ScrnInfoRec, and it
          takes care of initialising fields to defined ``unused''
          values.

          Claim the entities for each instance of the hardware
          found.  This prevents other drivers from claiming the
          same hardware.

          Must leave hardware in the same state it found it in, and
          must not do any hardware initialisation.

          All detection can be overridden via the config file, and
          that parsed information is available to the driver at
          this stage.

          Returns TRUE if one or more instances are found, and
          FALSE otherwise.

     int xf86MatchDevice(const char *drivername,

               GDevPtr **driversectlist)

          This function takes the name of the driver and returns
          via driversectlist a list of device sections that match
          the driver name.  The function return value is the number
          of matches found.  If a fatal error is encountered the
          return value is -1.

          The caller should use xfree() to free *driversectlist
          when it is no longer needed.

     ScrnInfoPtr xf86AllocateScreen(DriverPtr drv, int flags)

          This function allocates a new ScrnInfoRec in the
          xf86Screens[] array.  This function is normally called by
          the video driver ChipProbe() functions.  The return value
          is a pointer to the newly allocated ScrnInfoRec.  The
          scrnIndex, origIndex, module and drv fields are ini-
          tialised.  The reference count in drv is incremented.
          The storage for any currently allocated ``privates''
          pointers is also allocated and the privates field ini-
          tialised (the privates data is of course not allocated or
          initialised).  This function never returns on failure.
          If the allocation fails, the server exits with a fatal
          error.  The flags value is not currently used, and should
          be set to zero.

At the completion of this, a list of ScrnInfoRecs have been allocated in the
xf86Screens[] array, and the associated entities and fixed resources have
been claimed.  The following ScrnInfoRec fields must be initialised at this
point:

                    driverVersion
                    driverName
                    scrnIndex(*)
                    origIndex(*)
                    drv(*)
                    module(*)
                    name
                    Probe
                    PreInit
                    ScreenInit
                    EnterVT
                    LeaveVT
                    numEntities
                    entityList
                    access

(*) These are initialised when the ScrnInfoRec is allocated, and not explic-
itly by the driver.

The following ScrnInfoRec fields must be initialised if the driver is going
to use them:

                    SwitchMode
                    AdjustFrame
                    FreeScreen
                    ValidMode

5.9  Matching Screens

This is done at the start of the first server generation only.

After the Probe phase is finished, there will be some number of ScrnInfoRecs.
These are then matched with the active Screen sections in the XF86Config, and
those not having an active Screen section are deleted.  If the number of
remaining screens is 0, InitOutput() sets screenInfo.numScreens to 0 and
returns.

At this point the following fields of the ScrnInfoRecs must be initialised:

                    confScreen

5.10  Allocate non-conflicting resources

This is done at the start of the first server generation only.

Before calling the drivers again, the resource information collected from the
Probe phase is processed.  This includes checking the extent of PCI resources
for the probed devices, and resolving any conflicts in the relocatable PCI
resources.  It also reports conflicts, checks bus routing issues, and any-
thing else that is needed to enable the entities for the next phase.

If any drivers registered an EntityInit() function during the Probe phase,
then they are called here.

5.11  Sort the Screens and pre-check Monitor Information

This is done at the start of the first server generation only.

The list of screens is sorted to match the ordering requested in the config
file.

The list of modes for each active monitor is checked against the monitor's
parameters.  Invalid modes are pruned.

5.12  PreInit

This is done at the start of the first server generation only.

For each ScrnInfoRec, enable access to the screens entities and call the
ChipPreInit() function.

     Bool ChipPreInit(ScrnInfoRec screen, int flags)

          The purpose of this function is to find out all the
          information required to determine if the configuration is
          usable, and to initialise those parts of the ScrnInfoRec
          that can be set once at the beginning of the first server
          generation.

          The number of entities registered for the screen should
          be checked against the expected number (most drivers
          expect only one).  The entity information for each of
          them should be retrieved (with xf86GetEntityInfo()) and
          checked for the correct bus type and that none of the
          sharable resources registered during the Probe phase was
          rejected.

          Access to resources for the entities that can be con-
          trolled in a device-independent way are enabled before
          this function is called.  If the driver needs to access
          any resources that it has disabled in an EntityInit()
          function that it registered, then it may enable them here
          providing that it disables them before this function
          returns.

          This includes probing for video memory, clocks, ramdac,
          and all other HW info that is needed.  It includes deter-
          mining the depth/bpp/visual and related info.  It
          includes validating and determining the set of video
          modes that will be used (and anything that is required to
          determine that).

          This information should be determined in the least intru-
          sive way possible.  The state of the HW must remain
          unchanged by this function.  Although video memory
          (including MMIO) may be mapped within this function, it
          must be unmapped before returning.  Driver specific
          information should be stored in a structure hooked into
          the ScrnInfoRec's driverPrivate field.  Any other modules
          which require persistent data (ie data that persists
          across server generations) should be initialised in this
          function, and they should allocate a ``privates'' index
          to hook their data into by calling xf86AllocateScrnInfo-
          PrivateIndex().  The ``privates'' data is persistent.

          Helper functions for some of these things are provided at
          the XFree86 common level, and the driver can choose to
          make use of them.

          All additional resources that the screen needs must be
          registered here.  This should be done with xf86Register-
          Resources().  If some of the fixed resources registered
          in the Probe phase are not needed or not decoded by the
          hardware when in the OPERATING server state, their status
          should be updated with xf86SetOperatingState().

          Modules may be loaded at any point in this function, and
          all modules that the driver will need must be loaded
          before the end of this function.  The xf86LoadSubModule()
          function should be used to load modules.  A driver may
          unload a module within this function if it was only
          needed temporarily, and the UnloadSubModule() function
          should be used to do that.  Otherwise there is no need to
          explicitly unload modules because the loader takes care
          of module dependencies and will unload submodules auto-
          matically if/when the driver module is unloaded.

          The bulk of the ScrnInfoRec fields should be filled out
          in this function.

          ChipPreInit() returns FALSE when the configuration is
          unusable in some way (unsupported depth, no valid modes,
          not enough video memory, etc), and TRUE if it is usable.

          It is expected that if the ChipPreInit() function returns
          TRUE, then the only reasons that subsequent stages in the
          driver might fail are lack or resources (like xalloc
          failures).  All other possible reasons for failure should
          be determined by the ChipPreInit() function.

The ScrnInfoRecs for screens where the ChipPreInit() fails are removed.  If
none remain, InitOutput() sets screenInfo.numScreens to 0 and returns.

At this point, further fields of the ScrnInfoRecs would normally be filled
in.  Most are not strictly mandatory, but many are required by other layers
and/or helper functions that the driver may choose to use.  The documentation
for those layers and helper functions indicates which they require.

The following fields of the ScrnInfoRecs should be filled in if the driver is
going to use them:

                    monitor
                    display
                    depth
                    pixmapBPP
                    bitsPerPixel
                    weight                (>8bpp only)
                    mask                  (>8bpp only)
                    offset                (>8bpp only)
                    rgbBits               (8bpp only)
                    gamma
                    defaultVisual
                    maxHValue
                    maxVValue
                    virtualX
                    virtualY
                    displayWidth
                    frameX0
                    frameY0
                    frameX1
                    frameY1
                    zoomLocked
                    modePool
                    modes
                    currentMode
                    progClock             (TRUE if clock is programmable)
                    chipset
                    ramdac
                    clockchip
                    numClocks             (if not programmable)
                    clock[]               (if not programmable)
                    videoRam
                    biosBase
                    memBase
                    memClk
                    driverPrivate
                    chipID
                    chipRev

     pointer xf86LoadSubModule(ScrnInfoPtr pScrn, const char *name):

          Load a module that a driver depends on.  This function
          loads the module name as a sub module of the driver.  The
          return value is a handle identifying the new module.  If
          the load fails, the return value will be NULL.  If a
          driver needs to explicitly unload a module it has loaded
          in this way, the return value must be saved and passed to
          UnloadSubModule() when unloading.

     void UnloadSubModule(pointer module)

          Unloads the module referenced by module.  module should
          be a pointer returned previously by xf86LoadSubModule().

5.13  Cleaning up Unused Drivers

At this point it is known which screens will be in use, and which drivers are
being used.  Unreferenced drivers (and modules they may have loaded) are
unloaded here.

5.14  Consistency Checks

The parameters that must be global to the server, like pixmap formats, bitmap
bit order, bitmap scanline unit and image byte order are compared for each of
the screens.  If a mismatch is found, the server exits with an appropriate
message.

5.15  Check if Resource Control is Needed

Determine if resource access control is needed.  This is the case if more
than one screen is used.  If necessary the RAC wrapper module is loaded.

5.16  AddScreen (ScreenInit)

At this point, the valid screens are known.  AddScreen() is called for each
of them, passing ChipScreenInit() as the argument.  AddScreen() is a DIX
function that allocates a new screenInfo.screen[] entry (aka pScreen), and
does some basic initialisation of it.  It then calls the ChipScreenInit()
function, with pScreen as one of its arguments.  If ChipScreenInit() returns
FALSE, AddScreen() returns -1.  Otherwise it returns the index of the screen.
AddScreen() should only fail because of programming errors or failure to
allocate resources (like memory).  All configuration problems should be
detected BEFORE this point.

     Bool ChipScreenInit(int index, ScreenPtr pScreen,

               int argc, char **argv)

          This is called at the start of each server generation.

          Fill in all of pScreen, possibly doing some of this by
          calling ScreenInit functions from other layers like mi,
          framebuffers (cfb, etc), and extensions.

          Decide which operations need to be placed under resource
          access control.  The classes of operations are the frame
          buffer operations (RAC_FB), the pointer operations
          (RAC_CURSOR), the viewport change operations (RAC_VIEW-
          PORT) and the colormap operations (RAC_COLORMAP).  Any
          operation that requires resources which might be disabled
          during OPERATING state should be set to use RAC.  This
          can be specified separately for memory and IO resources
          (the racMemFlags and racIoFlags fields of the ScrnInfoRec
          respectively).

          Map any video memory or other memory regions.

          Save the video card state.  Enough state must be saved so
          that the original state can later be restored.

          Initialise the initial video mode.  The ScrnInfoRec's
          vtSema field should be set to TRUE just prior to changing
          the video hardware's state.

The ChipScreenInit() function (or functions from other layers that it calls)
should allocate entries in the ScreenRec's devPrivates area by calling Allo-
cateScreenPrivateIndex() if it needs per-generation storage.  Since the
ScreenRec's devPrivates information is cleared for each server generation,
this is the correct place to initialise it.

After AddScreen() has successfully returned, the following ScrnInfoRec fields
are initialised:

                    pScreen
                    racMemFlags
                    racIoFlags

The ChipScreenInit() function should initialise the CloseScreen and Save-
Screen fields of pScreen.  The old value of pScreen->CloseScreen should be
saved as part of the driver's per-screen private data, allowing it to be
called from ChipCloseScreen().  This means that the existing CloseScreen()
function is wrapped.

5.17  Finalising RAC Initialisation

After all the ChipScreenInit() functions have been called, each screen has
registered its RAC requirements.  This information is used to determine which
shared resources are requested by more than one driver and set the access
functions accordingly.  This is done following these rules:

  1.  The sharable resources registered by each entity are compared.  If a
      resource is registered by more than one entity the entity will be
      marked to indicate that it needs to share this resources type (IO or
      MEM).

  2.  A resource marked ``disabled'' during OPERATING state will be ignored
      entirely.

  3.  A resource marked ``unused'' will only conflict with an overlapping
      resource of an other entity if the second is actually in use during
      OPERATING state.

  4.  If an ``unused'' resource was found to conflict but the entity does not
      use any other resource of this type the entire resource type will be
      disabled for that entity.

5.18  Finishing InitOutput()

At this point InitOutput() is finished, and all the screens have been setup
in their initial video mode.

5.19  Mode Switching

When a SwitchMode event is received, ChipSwitchMode() is called (when it
exists):

     Bool ChipSwitchMode(int index, DisplayModePtr mode, int flags)

          Initialises the new mode for the screen identified by
          index;.  The viewport may need to be adjusted also.

5.20  Changing Viewport

When a Change Viewport event is received, ChipAdjustFrame() is called (when
it exists):

     void ChipAdjustFrame(int index, int x, int y, int flags)

          Changes the viewport for the screen identified by index;.

5.21  VT Switching

When a VT switch event is received, xf86VTSwitch() is called.  xf86VTSwitch()
does the following:

      On ENTER:

               o enable port I/O access

               o save and initialise the bus/resource state

               o enter the SETUP server state

               o calls ChipEnterVT() for each screen

               o enter the OPERATING server state

               o validate GCs

               o Restore fb from saved pixmap for each screen

               o Enable all input devices

      On LEAVE:

               o Save fb to pixmap for each screen

               o validate GCs

               o enter the SETUP server state

               o calls ChipLeaveVT() for each screen

               o disable all input devices

               o restore bus/resource state

               o disables port I/O access

     Bool ChipEnterVT(int index, int flags)

          This function should initialise the current video mode
          and initialise the viewport, turn on the HW cursor if
          appropriate, etc.

          Should it re-save the video state before initialising the
          video mode?

     void ChipLeaveVT(int index, int flags)

          This function should restore the saved video state.  If
          appropriate it should also turn off the HW cursor, and
          invalidate any pixmap/font caches.

     Optionally, ChipLeaveVT() may also unmap memory regions.  If so,
     ChipEnterVT() will need to remap them.  Additionally, if an aper-
     ture used to access video memory is unmapped and remapped in this
     fashion, ChipEnterVT() will also need to notify the framebuffer
     layers of the aperture's new location in virtual memory.  This is
     done with a call to the screen's ModifyPixmapHeader() function, as
     follows

          (*pScreen->ModifyPixmapHeader)(pScrn->ppix,

                    -1, -1, -1, -1, -1, NewApertureAddress);

               where the ``ppix'' field in a ScrnInfoRec
               points to the pixmap used by the screen's
               SaveRestoreImage() function to hold the
               screen's contents while switched out.

     Currently, aperture remapping, as described here, should not be
     attempted if the driver uses the xf8_16bpp or xf8_32bpp framebuffer
     layers.  A pending restructuring of VT switching will address this
     restriction in the near future.

Other layers may wrap the ChipEnterVT() and ChipLeaveVT() functions if they
need to take some action when these events are received.

5.22  End of server generation

At the end of each server generation, the DIX layer calls ChipCloseScreen()
for each screen:

     Bool ChipCloseScreen(int index, ScreenPtr pScreen)

          This function should restore the saved video state and
          unmap the memory regions.

          It should also free per-screen data structures allocated
          by the driver.  Note that the persistent data held in the
          ScrnInfoRec's driverPrivate field should not be freed
          here because it is needed by subsequent server genera-
          tions.

          The ScrnInfoRec's vtSema field should be set to FALSE
          once the video HW state has been restored.

          Before freeing the per-screen driver data the saved Clos-
          eScreen value should be restored to pScreen->CloseScreen,
          and that function should be called after freeing the
          data.

6.  Optional Driver Functions

The functions outlined here can be called from the XFree86 common layer, but
their presence is optional.

6.1  Mode Validation

When a mode validation helper supplied by the XFree86-common layer is being
used, it can be useful to provide a function to check for hw specific mode
constraints:

     ModeStatus ChipValidMode(int index, DisplayModePtr mode,

               Bool verbose, int flags)

          Check the passed mode for hw-specific constraints, and
          return the appropriate status value.

This function may also modify the effective timings and clock of the passed
mode.  These have been stored in the mode's Crtc* and SynthClock elements,
and have already been adjusted for interlacing, doublescanning, multiscanning
and clock multipliers and dividers.  The function should not modify any other
mode field, unless it wants to modify the mode timings reported to the user
by xf86PrintModes().

The function is called once for every mode in the XF86Config Monitor section
assigned to the screen, with flags set to MODECHECK_INITIAL.  It is subse-
quently called for every mode in the XF86Config Display subsection assigned
to the screen, with flags set to MODECHECK_FINAL.  In the second case, the
mode will have successfully passed all other tests.  In addition, the ScrnIn-
foRec's virtualX, virtualY and displayWidth fields will have been set as if
the mode to be validated were to be the last mode accepted.

In effect, calls with MODECHECK_INITIAL are intended for checks that do not
depend on any mode other than the one being validated, while calls with MOD-
ECHECK_FINAL are intended for checks that may involve more than one mode.

6.2  Free screen data

When a screen is deleted prior to the completion of the ScreenInit phase the
ChipFreeScreen() function is called when defined.

     void ChipFreeScreen(int scrnindex, int flags)

          Free any driver-allocated data that may have been allo-
          cated up to and including an unsuccessful Chip-
          ScreenInit() call.  This would predominantly be data
          allocated by ChipPreInit() that persists across server
          generations.  It would include the driverPrivate, and any
          ``privates'' entries that modules may have allocated.

7.  Recommended driver functions

The functions outlined here are for internal use by the driver only.  They
are entirely optional, and are never accessed directly from higher layers.
The sample function declarations shown here are just examples.  The interface
(if any) used is up to the driver.

7.1  Save

Save the video state.  This could be called from ChipScreenInit() and (possi-
bly) ChipEnterVT().

     void ChipSave(ScrnInfoPtr pScrn)

          Saves the current state.  This will only be saving pre-
          server states or states before returning to the server.
          There is only one current saved state per screen and it
          is stored in private storage in the screen.

7.2  Restore

Restore the original video state.  This could be called from the
ChipLeaveVT() and ChipCloseScreen() functions.

     void ChipRestore(ScrnInfoPtr pScrn)

          Restores the saved state from the private storage.  Usu-
          ally only used for restoring text modes.

7.3  Initialise Mode

Initialise a video mode.  This could be called from the ChipScreenInit(),
ChipSwitchMode() and ChipEnterVT() functions.

     Bool ChipModeInit(ScrnInfoPtr pScrn, DisplayModePtr mode)

          Programs the hardware for the given video mode.

8.  Data and Data Structures

8.1  Command line data

Command line options are typically global, and are stored in global vari-
ables.  These variables are read-only and are available to drivers via a
function call interface.  Most of these command line values are processed via
helper functions to ensure that they are treated consistently by all drivers.
The other means of access is provided for cases where the supplied helper
functions might not be appropriate.

Some of them are:

              xf86Verbose               verbosity level
              xf86Bpp                   -bpp from the command line
              xf86Depth                 -depth from the command line
              xf86Weight                -weight from the command line
              xf86Gamma                 -{r,g,b,}gamma from the command line
              xf86FlipPixels            -flippixels from the command line
              xf86ProbeOnly             -probeonly from the command line
              defaultColorVisualClass   -cc from the command line

If we ever do allow for screen-specific command line options, we may need to
rethink this.

These can be accessed in a read-only manner by drivers with the following
functions:

     int xf86GetVerbosity()

          Returns the value of xf86Verbose.

     int xf86GetDepth()

          Returns the -depth command line setting.  If not set on
          the command line, -1 is returned.

     rgb xf86GetWeight()

          Returns the -weight command line setting.  If not set on
          the command line, {0, 0, 0} is returned.

     Gamma xf86GetGamma()

          Returns the -gamma or -rgamma, -ggamma, -bgamma command
          line settings.  If not set on the command line, {0.0,
          0.0, 0.0} is returned.

     Bool xf86GetFlipPixels()

          Returns TRUE if -flippixels is present on the command
          line, and FALSE otherwise.

     const char *xf86GetServerName()

          Returns the name of the X server from the command line.

8.2  Data handling

Config file data contains parts that are global, and parts that are Screen
specific.  All of it is parsed into data structures that neither the drivers
or most other parts of the server need to know about.

The global data is typically not required by drivers, and as such, most of it
is stored in the private xf86InfoRec.

The screen-specific data collected from the config file is stored in screen,
device, display, monitor-specific data structures that are separate from the
ScrnInfoRecs, with the appropriate elements/fields hooked into the ScrnIn-
foRecs as required.  The screen config data is held in confScreenRec, device
data in the GDevRec, monitor data in the MonRec, and display data in the Dis-
pRec.

The XFree86 common layer's screen specific data (the actual data in use for
each screen) is held in the ScrnInfoRecs.  As has been outlined above, the
ScrnInfoRecs are allocated at probe time, and it is the responsibility of the
Drivers' Probe() and PreInit() functions to finish filling them in based on
both data provided on the command line and data provided from the Config
file.  The precedence for this is:

     command line  ->  config file  ->  probed/default data

For most things in this category there are helper functions that the drivers
can use to ensure that the above precedence is consistently used.

As well as containing screen-specific data that the XFree86 common layer
(including essential parts of the server infrastructure as well as helper
functions) needs to access, it also contains some data that drivers use
internally.  When considering whether to add a new field to the ScrnInfoRec,
consider the balance between the convenience of things that lots of drivers
need and the size/obscurity of the ScrnInfoRec.

Per-screen driver specific data that cannot be accommodated with the static
ScrnInfoRec fields is held in a driver-defined data structure, a pointer to
which is assigned to the ScrnInfoRec's driverPrivate field.  This is per-
screen data that persists across server generations (as does the bulk of the
static ScrnInfoRec data).  It would typically also include the video card's
saved state.

Per-screen data for other modules that the driver uses (for example, the XAA
module) that is reset for each server generation is hooked into the ScrnIn-
foRec through it's privates field.

Once it has stabilised, the data structures and variables accessible to video
drivers will be documented here.  In the meantime, those things defined in
the xf86.h and xf86str.h files are visible to video drivers.  Things defined
in xf86Priv.h and xf86Privstr.h are NOT intended to be visible to video
drivers, and it is an error for a driver to include those files.

8.3  Accessing global data

Some other global state information that the drivers may access via functions
is as follows:

     Bool xf86ServerIsExiting()

          Returns TRUE if the server is at the end of a generation
          and is in the process of exiting, and FALSE otherwise.

     Bool xf86ServerIsResetting()

          Returns TRUE if the server is at the end of a generation
          and is in the process of resetting, and FALSE otherwise.

     Bool xf86ServerIsInitialising()

          Returns TRUE if the server is at the beginning of a gen-
          eration and is in the process of initialising, and FALSE
          otherwise.

     Bool xf86ServerIsOnlyProbing()

          Returns TRUE if the -probeonly command line flag was
          specified, and FALSE otherwise.

     Bool xf86CaughtSignal()

          Returns TRUE if the server has caught a signal, and FALSE
          otherwise.

8.4  Allocating private data

A driver and any module it uses may allocate per-screen private storage in
either the ScreenRec (DIX level) or ScrnInfoRec (XFree86 common layer level).
ScreenRec storage persists only for a single server generation, and ScrnIn-
foRec storage persists across generations for the lifetime of the server.

The ScreenRec devPrivates data must be reallocated/initialised at the start
of each new generation.  This is normally done from the ChipScreenInit()
function, and Init functions for other modules that it calls.  Data allocated
in this way should be freed by the driver's ChipCloseScreen() functions, and
Close functions for other modules that it calls.  A new devPrivates entry is
allocated by calling the AllocateScreenPrivateIndex() function.

     int AllocateScreenPrivateIndex()

          This function allocates a new element in the devPrivates
          field of all currently existing ScreenRecs.  The return
          value is the index of this new element in the devPrivates
          array.  The devPrivates field is of type DevUnion:

                       typedef union _DevUnion {
                           pointer             ptr;
                           long                val;
                           unsigned long       uval;
                           pointer             (*fptr)(void);
                       } DevUnion;

          which allows the element to be used for any of the above
          types.  It is commonly used as a pointer to data that the
          caller allocates after the new index has been allocated.

          This function will return -1 when there is an error allo-
          cating the new index.

The ScrnInfoRec privates data persists for the life of the server, so only
needs to be allocated once.  This should be done from the ChipPreInit() func-
tion, and Init functions for other modules that it calls.  Data allocated in
this way should be freed by the driver's ChipFreeScreen() functions, and Free
functions for other modules that it calls.  A new privates entry is allocated
by calling the xf86AllocateScrnInfoPrivateIndex() function.

     int xf86AllocateScrnInfoPrivateIndex()

          This function allocates a new element in the privates
          field of all currently existing ScrnInfoRecs.  The return
          value is the index of this new element in the privates
          array.  The privates field is of type DevUnion:

                       typedef union _DevUnion {
                           pointer             ptr;
                           long                val;
                           unsigned long       uval;
                           pointer             (*fptr)(void);
                       } DevUnion;

          which allows the element to be used for any of the above
          types.  It is commonly used as a pointer to data that the
          caller allocates after the new index has been allocated.

          This function will not return when there is an error
          allocating the new index.  When there is an error it will
          cause the server to exit with a fatal error.  The similar
          function for allocation privates in the ScreenRec (Allo-
          cateScreenPrivateIndex()) differs in this respect by
          returning -1 when the allocation fails.

9.  Keeping Track of Bus Resources

9.1  Theory of Operation

The XFree86 common layer has knowledge of generic access control mechanisms
for devices on certain bus systems (currently the PCI bus) as well as of
methods to enable or disable access to the buses itself.  Furthermore it can
access information on resources decoded by these devices and if necessary
modify it.

When first starting the Xserver collects all this information, saves it for
restoration, checks it for consistency, and if necessary, corrects it.
Finally it disables all resources on a generic level prior to calling any
driver function.

When the Probe() function of each driver is called the device sections are
matched against the devices found in the system.  The driver may probe
devices at this stage that cannot be identified by using device independent
methods.  Access to all resources that can be controlled in a device indepen-
dent way is disabled.  The Probe() function should register all non-relocat-
able resources at this stage.  If a resource conflict is found between exclu-
sive resources the driver will fail immediately.  Optionally the driver might
specify an EntityInit(), EntityLeave() and EntityEnter() function.

EntityInit() can be used to disable any shared resources that are not con-
trolled by the generic access control functions.  It is called prior to the
PreInit phase regardless if an entity is active or not.  When calling the
EntityInit(), EntityEnter() and EntityLeave() functions the common level will
disable access to all other entities on a generic level.  Since the common
level has no knowledge of device specific methods to disable access to
resources it cannot be guaranteed that certain resources are not decoded by
any other entity until the EntityInit() or EntityEnter() phase is finished.
Device drivers should therefore register all those resources which they are
going to disable.  If these resources are never to be used by any driver
function they may be flagged ResInit so that they can be removed from the
resource list after processing all EntityInit() functions.  EntityEnter()
should disable decoding of all resources which are not registered as exclu-
sive and which are not handled by the generic access control in the common
level.  The difference to EntityInit() is that the latter one is only called
once during lifetime of the server.  It can therefore be used to set up vari-
ables prior to disabling resources.  EntityLeave() should restore the origi-
nal state when exiting the server or switching to a different VT.  It also
needs to disable device specific access functions if they need to be disabled
on server exit or VT switch.  The default state is to enable them before giv-
ing up the VT.

In PreInit() phase each driver should check if any sharable resources it has
registered during Probe() has been denied and take appropriate action which
could simply be to fail.  If it needs to access resources it has disabled
during EntitySetup() it can do so provided it has registered these and will
disable them before returning from PreInit().  This also applies to all other
driver functions.  Several functions are provided to request resource ranges,
register these, correct PCI config space and add replacements for the generic
access functions.  Resources may be marked ``disabled'' or ``unused'' during
OPERATING stage.  Although these steps could also be performed in
ScreenInit(), this is not desirable.

Following PreInit() phase the common level determines if resource access con-
trol is needed.  This is the case if more than one screen is used.  If neces-
sary the RAC wrapper module is loaded.  In ScreenInit() the drivers can
decide which operations need to be placed under RAC.  Available are the frame
buffer operations, the pointer operations and the colormap operations.  Any
operation that requires resources which might be disabled during OPERATING
state should be set to use RAC.  This can be specified separately for memory
and IO resources.

When ScreenInit() phase is done the common level will determine which shared
resources are requested by more than one driver and set the access functions
accordingly.  This is done following these rules:

  1.  The sharable resources registered by each entity are compared.  If a
      resource is registered by more than one entity the entity will be
      marked to need to share this resources type (IO or MEM).

  2.  A resource marked ``disabled'' during OPERATING state will be ignored
      entirely.

  3.  A resource marked ``unused'' will only conflicts with an overlapping
      resource of an other entity if the second is actually in use during
      OPERATING state.

  4.  If an ``unused'' resource was found to conflict however the entity does
      not use any other resource of this type the entire resource type will
      be disabled for that entity.

The driver has the choice among different ways to control access to certain
resources:

  1.  It can rely on the generic access functions.  This is probably the most
      common case.  Here the driver only needs to register any resource it is
      going to use.

  2.  It can replace the generic access functions by driver specific ones.
      This will mostly be used in cases where no generic access functions are
      available.  In this case the driver has to make sure these resources
      are disabled when entering the PreInit() stage.  Since the replacement
      functions are registered in PreInit() the driver will have to enable
      these resources itself if it needs to access them during this state.
      The driver can specify if the replacement functions can control memory
      and/or I/O resources separately.

  3.  The driver can enable resources itself when it needs them.  Each driver
      function enabling them needs to disable them before it will return.
      This should be used if a resource which can be controlled in a device
      dependent way is only required during SETUP state.  This way it can be
      marked ``unused'' during OPERATING state.

A resource which is decoded during OPERATING state however never accessed by
the driver should be marked unused.

Since access switching latencies are an issue during Xserver operation, the
common level attempts to minimize the number of entities that need to be
placed under RAC control.  When a wrapped operation is called, the EnableAc-
cess() function is called before control is passed on.  EnableAccess() checks
if a screen is under access control.  If not it just establishes bus routing
and returns.  If the screen needs to be under access control, EnableAccess()
determines which resource types (MEM, IO) are required.  Then it tests if
this access is already established.  If so it simply returns.  If not it dis-
ables the currently established access, fixes bus routing and enables access
to all entities registered for this screen.

Whenever a mode switch or a VT-switch is performed the common level will
return to SETUP state.

9.2  Resource Types

Resource have certain properties.  When registering resources each range is
accompanied by a flag consisting of the ORed flags of the different proper-
ties the resource has.  Each resource range may be classified according to

   o its physical properties i.e., if it addresses memory (ResMem)  or I/O
     space (ResIo),

   o if it addresses a block (ResBlock) or sparse (ResSparse) range,

   o its access properties.

There are two known access properties:

   o ResExclusive for resources which may not be shared with any other device
     and

   o ResShared for resources which can be disabled and therefore can be
     shared.

If it is necessary to test a resource against any type a generic access type
ResAny is provided.  If this is set the resource will conflict with any
resource of a different entity intersecting its range.  Further it can be
specified that a resource is decoded however never used during any stage
(ResUnused) or during OPERATING state (ResUnusedOpr).  A resource only visi-
ble during the init functions (ie.  EntityInit(), EntityEnter() and
EntityLeave() should be registered with the flag ResInit.  A resource that
might conflict with background resource ranges may be flagged with ResBios.
This might be useful when registering resources ranges that were assigned by
the system Bios.

Several predefined resource lists are available for VGA and 8514/A resources
in common/xf86Resources.h.

9.3  Available Functions

The functions provided for resource management are listed in their order of
use in the driver.

9.3.1  Probe Phase

In this phase each driver detects those resources it is able to drive, cre-
ates an entity record for each of them, registers non-relocatable resources
and allocates screens and adds the resources to screens.

Two helper functions are provided for matching device sections in the
XF86Config file to the devices:

     int xf86MatchPciInstances(const char *driverName, int vendorID,

               SymTabPtr chipsets, PciChipsets *PCIchipsets,

               GDevPtr *devList, int numDevs,

               GDevPtr *devList, int numDevs, DriverPtr drvp,

               int **foundEntities)

          This function finds matches between PCI cards that a
          driver supports and config file device sections.  It is
          intended for use in the ChipProbe() function of drivers
          for PCI cards.  Only probed PCI devices with a vendor ID
          matching vendorID are considered.  devList and numDevs
          are typically those found from calling xf86MatchDevice(),
          and represent the active config file device sections rel-
          evant to the driver.  PCIchipsets is a table that pro-
          vides a mapping between the PCI device IDs, the driver's
          internal chipset tokens and a list of fixed resources.

          When a device section doesn't have a BusID entry it can
          only match the primary video device.  Secondary devices
          are only matched with device sections that have a match-
          ing BusID entry.

          Once the preliminary matches have been found, a final
          match is confirmed by checking if the chipset override,
          ChipID override or probed PCI chipset type match one of
          those given in the chipsets and PCIchipsets lists.  The
          PCIchipsets list includes a list of the PCI device IDs
          supported by the driver.  The list should be terminated
          with an entry with PCI ID -1".  The chipsets list is a
          table mapping the driver's internal chipset tokens to
          names, and should be terminated with a NULL entry.  Only
          those entries with a corresponding entry in the PCI-
          chipsets list are considered.  The order of precedence
          is: config file chipset, config file ChipID, probed PCI
          device ID.

          In cases where a driver handles PCI chipsets with more
          than one vendor ID, it may set vendorID to 0, and OR each
          devID in the list with (the vendor ID << 16).

          Entity index numbers for confirmed matches are returned
          as an array via foundEntities.  The PCI information,
          chipset token and device section for each match are found
          in the EntityInfoRec referenced by the indices.

          The function return value is the number of confirmed
          matches.  A return value of -1 indicates an internal
          error.  The returned foundEntities array should be freed
          by the driver with xfree() when it is no longer needed in
          cases where the return value is greater than zero.

     int xf86MatchIsaInstances(const char *driverName,

               SymTabPtr chipsets, IsaChipsets *ISAchipsets,

               DriverPtr drvp, FindIsaDevProc FindIsaDevice,

               GDevPtr *devList, int numDevs, int **foundEntities)

          This function finds matches between ISA cards that a
          driver supports and config file device sections.  It is
          intended for use in the ChipProbe() function of drivers
          for ISA cards.  devList and numDevs are typically those
          found from calling xf86MatchDevice(), and represent the
          active config file device sections relevant to the
          driver.  ISAchipsets is a table that provides a mapping
          between the driver's internal chipset tokens and the
          resource classes.  FindIsaDevice is a driver-provided
          function that probes the hardware and returns the chipset
          token corresponding to what was detected, and -1 if noth-
          ing was detected.

          If the config file device section contains a chipset
          entry, then it is checked against the chipsets list.
          When no chipset entry is present, the FindIsaDevice func-
          tion is called instead.

          Entity index numbers for confirmed matches are returned
          as an array via foundEntities.  The chipset token and
          device section for each match are found in the EntityIn-
          foRec referenced by the indices.

          The function return value is the number of confirmed
          matches.  A return value of -1 indicates an internal
          error.  The returned foundEntities array should be freed
          by the driver with xfree() when it is no longer needed in
          cases where the return value is greater than zero.

These two helper functions make use of several core functions that are avail-
able at the driver level:

     Bool xf86ParsePciBusString(const char *busID, int *bus,

               int *device, int *func)

          Takes a BusID string, and if it is in the correct format,
          returns the PCI bus, device, func values that it indi-
          cates.  The format of the string is expected to be
          "PCI:bus:device:func" where each of `bus', `device' and
          `func' are decimal integers.  The ":func" part may be
          omitted, and the func value assumed to be zero, but this
          isn't encouraged.  The "PCI" prefix may also be omitted.
          The prefix "AGP" is currently equivalent to the "PCI"
          prefix.  If the string isn't a valid PCI BusID, the
          return value is FALSE.

     Bool xf86ComparePciBusString(const char *busID, int bus,

               int device, int func)

          Compares a BusID string with PCI bus, device, func val-
          ues.  If they match TRUE is returned, and FALSE if they
          don't.

     Bool xf86ParseIsaBusString(const char *busID)

          Compares a BusID string with the ISA bus ID string ("ISA"
          or "ISA:").  If they match TRUE is returned, and FALSE if
          they don't.

     Bool xf86CheckPciSlot(int bus, int device, int func)

          Checks if the PCI slot bus:device:func has been claimed.
          If so, it returns FALSE, and otherwise TRUE.

     int xf86ClaimPciSlot(int bus, int device, int func, DriverPtr drvp,

               int chipset, GDevPtr dev, Bool active)

          This function is used to claim a PCI slot, allocate the
          associated entity record and initialise their data struc-
          tures.  The return value is the index of the newly allo-
          cated entity record, or -1 if the claim fails.  This
          function should always succeed if xf86CheckPciSlot()
          returned TRUE for the same PCI slot.

     Bool xf86IsPrimaryPci(void)

          This function returns TRUE if the primary card is a PCI
          device, and FALSE otherwise.

     int xf86ClaimIsaSlot(DriverPtr drvp, int chipset,

               GDevPtr dev, Bool active)

          This allocates an entity record entity and initialise the
          data structures.  The return value is the index of the
          newly allocated entity record.

     Bool xf86IsPrimaryIsa(void)

          This function returns TRUE if the primary card is an ISA
          (non-PCI) device, and FALSE otherwise.

Two helper functions are provided to aid configuring entities:

     Bool xf86ConfigActivePciEntity(ScrnInfoPtr pScrn, int entityIndex,

               PciChipsets *p_chip, resList res,

               EntityProc init, EntityProc enter,

               EntityProc leave, pointer private)

     Bool xf86ConfigActiveIsaEntity(ScrnInfoPtr pScrn, int entityIndex,

               IsaChipsets *i_chip, resList res,

               EntityProc init, EntityProc enter,

               EntityProc leave, pointer private)

          These functions are used to register the non-relocatable
          resources for an entity, and the optional entity-specific
          Init, Enter and Leave functions.  Usually the list of
          fixed resources is obtained from the Isa/PciChipsets
          lists.  However an additional list of resources may be
          passed.  Generally this is not required.  The return
          value is TRUE when successful.  The init, enter, leave
          functions are defined as follows:

               typedef void (*EntityProc)(int entityIndex,

                         pointer private)

          They are passed the entity index and a pointer to a pri-
          vate scratch area.  This are can be set up during Probe()
          and its address can be passed to xf86ConfigActiveIsaEn-
          tity() xf86ConfigActivePciEntity() as the last argument.

These two helper functions make use of several core functions that are avail-
able at the driver level:

     void xf86ClaimFixedResources(resList list, int entityIndex)

          This function registers the non-relocatable resources
          which cannot be disabled and which therefore would cause
          the server to fail immediately if they were found to con-
          flict.  It also records non-relocatable but sharable
          resources for processing after the Probe() phase.

     Bool xf86SetEntityFuncs(int entityIndex, EntityProc init,

               EntityProc enter, EntityProc leave, pointer)

          This function registers with an entity the init, enter,
          leave functions along with the pointer to their private
          area.

     void xf86AddEntityToScreen(ScrnInfoPtr pScrn, int entityIndex)

          This function associates the entity referenced by enti-
          tyIndex with the screen.

9.3.2  PreInit Phase

During this phase the remaining resource should be registered.  PreInit()
should call xf86GetEntityInfo() To obtain a pointer to an EntityInfoRec for
each entity it is able to drive and check if any resource are listed in its
resources field.  If resources registered in the Probe phase have been
rejected in the post-Probe phase (resources == NULL), then the driver should
decide if it can continue without using these or if it should fail.

     EntityInfoPtr xf86GetEntityInfo(int entityIndex)

          This function returns a pointer to the EntityInfoRec ref-
          erenced by entityIndex.  The returned EntityInfoRec
          should be freed with xfree() when no longer needed.

Several functions are provided to simplify resource registration:

     Bool xf86IsEntityPrimary(int entityIndex)

          This function returns TRUE if the entity referenced by
          entityIndex is the display device that primary display
          device (i.e., the one initialised at boot time and used
          in text mode).

     Bool xf86IsScreenPrimary(int scrnIndex)

          This function returns TRUE if the primary entity is reg-
          istered with the screen referenced by scrnIndex.

     pciVideoPtr xf86GetPciInfoForEntity(int entityIndex)

          This function returns a pointer to the pciVideoRec for
          the specified entity.  If the entity is not a PCI device,
          NULL is returned.

The primary function for registration of resources is:

     resPtr xf86RegisterResources(int entityIndex, resList list,

               int access)

          This function tries to register the resources in list.
          If list is NULL it tries to determine the resources auto-
          matically.  This only works for entities that provide a
          generic way to read out the resource ranges they decode.
          So far this is only the case for PCI devices.  By default
          the PCI resources are registered as shared (ResShared) if
          the driver wants to set a different access type it can do
          so by specifying the access flags in the third argument.
          A value of 0 means to use the default settings.  If for
          any reason the resource broker is not able to register
          some of the requested resources the function will return
          a pointer to a list of the failed ones.  In this case the
          driver may be able to move the resource to different
          locations.  In case of PCI bus entities this is done by
          passing the list of failed resources to xf86ReallocateP-
          ciResources().  When the registration succeeds, the
          return value is NULL.

     resPtr xf86ReallocatePciResources(int entityIndex, resPtr pRes)

          This function takes a list of PCI resources that need to
          be reallocated and returns a list of the reallocated
          resource.  This list needs to be passed to xf86Register-
          Resources() again to be registered with the broker.  If
          the reallocation fails, NULL is returned.

Two functions are provided to obtain a resource range of a given type:

     resRange xf86GetBlock(long type, memType size,

               memType window_start, memType window_end,

               memType align_mask, resPtr avoid)

          This function tries to find a block range of size size
          and type type in a window bound by window_start and win-
          dow_end with the alignment specified in align_mask.
          Optionally a list of resource ranges which should be
          avoided within the window can be supplied.  On failure a
          zero-length range of type ResEnd will be returned.

     resRange xf86GetSparse(long type,  memType fixed_bits,

               memType decode_mask, memType address_mask,

               resPtr avoid)

          This function is like the previous one, but attempts to
          find a sparse range instead of a block range.  Here three
          values have to be specified: the address_mask which marks
          all bits of the mask part of the address, the decode_mask
          which masks out the bits which are hardcoded and are
          therefore not available for relocation and the values of
          the fixed bits.  The function tries to find a base that
          satisfies the given condition.  If the function fails it
          will return a zero range of type ResEnd.  Optionally it
          might be passed a list of resource ranges to avoid.

Some PCI devices are broken in the sense that they return invalid size infor-
mation for a certain resource.  In this case the driver can supply the cor-
rect size and make sure that the resource range allocated for the card is
large enough to hold the address range decoded by the card.  The function
xf86FixPciResource() can be used to do this:

     Bool xf86FixPciResource(int entityIndex, unsigned int prt,

               CARD32 alignment, long type)

          This function fixes a PCI resource allocation.  The prt
          parameter contains the number of the PCI base register
          that needs to be fixed (0-5, and 6 for the BIOS base reg-
          ister).  The size is specified by the alignment.  Since
          PCI resources need to span an integral range of the size
          2^n the alignment also specifies the number of addresses
          that will be decoded.  If the driver specifies a type
          mask it can override the default type for PCI resources
          which is ResShared.  The resource broker needs to know
          that to find a matching resource range.  This function
          should be called before calling xf86RegisterResources().
          The return value is TRUE when the function succeeds.

     Bool xf86CheckPciMemBase(pciVideoPtr pPci, memType base)

          This function checks that the memory base address speci-
          fied matches one of the PCI base address register values
          for the given PCI device.  This is mostly used to check
          that an externally provided base address (e.g., from a
          config file) matches an actual value allocated to a
          device.

The driver may replace the generic access control functions for an entity by
it's own ones.  This is done with the xf86SetAccessFuncs():

     void xf86SetAccessFuncs(EntityInfoPtr pEnt, xf86AccessPtr p_io,

               xf86AccessPtr p_mem, xf86AccessPtr p_io_mem,

               xf86AccessPtr *ppAccessOld)

          The driver can pass three functions: one for I/O access,
          one for memory access and one for combined memory and I/O
          access.  If the memory access and combined access func-
          tions are identical the common level assumes that the
          memory access cannot be controlled independently of I/O
          access, if the I/O access function and the combined
          access functions are the same it is assumed that I/O can
          not be controlled independently.  If memory and I/O have
          to be controlled together all three values should be the
          same.  If a non NULL value is passed as fifth argument it
          is interpreted as an address where to store the old
          access record.  If the fifth argument is NULL it will be
          assumed that the generic access should be enabled before
          replacing the access functions.  Otherwise it will be
          disabled.  The driver may enable them itself using the
          returned values.  It should do this from his replacement
          access functions as the generic access may be disabled by
          the common level on certain occasions.  If replacement
          functions are specified they must control all resources
          of the specific type registered for the entity.

To find out if specific resource range is conflicting with another resource
the xf86ChkConflict() function may be used:

     memType xf86ChkConflict(resRange *rgp, int entityIndex)

          This function checks if the resource range rgp of for the
          specified entity conflicts with with another resource.
          If it a conflict is found, the address of the start of
          the conflict is returned.  The return value is zero when
          there is no conflict.

The OPERATING state properties of previously registered fixed resources can
be set with the xf86SetOperatingState() function:

     resPtr xf86SetOperatingState(resList list, int entityIndex,

               int mask)

          This function is used to set the status of a resource
          during OPERATING state.  list holds a list to which mask
          is to be applied.  The parameter mask may have the value
          ResUnusedOpr and ResDisableOpr.  The first one should be
          used if a resource isn't used by the driver during OPER-
          ATING state although it is decoded by the device, while
          the latter one indicates that the resource is not decoded
          during OPERATING state.  Note that the resource ranges
          have to match those specified during registration.  If a
          range has been specified starting at A and ending at B
          and suppose C us a value satisfying A < C < B one may not
          specify the resource range (A,B) by splitting it into two
          ranges (A,C) and (C,B).

The following two functions are provided for special cases:

     void xf86RemoveEntityFromScreen(ScrnInfoPtr pScrn, int entityIndex)

          This function may be used to remove an entity from a
          screen.  This only makes sense if a screen has more than
          one entity assigned or the screen is to be deleted.  No
          test is made if the screen has any entities left.

     void xf86DeallocateResourcesForEntity(int entityIndex, long type)

          This function deallocates all resources of a given type
          registered for a certain entity from the resource broker
          list.

9.3.3  ScreenInit Phase

All that is required in this phase is to setup the RAC flags.  Note that it
is also permissible to set these flags up in the PreInit phase.  The RAC
flags are held in the racIoFlags and racMemFlags fields of the ScrnInfoRec
for each screen.  They specify which graphics operations might require the
use of shared resources.  This can be specified separately for memory and I/O
resources.  The available flags are defined in rac/xf86RAC.h.  They are:

RAC_FB

     for framebuffer operations (including hw acceleration)

RAC_CURSOR

     for Cursor operations (??? I'm not sure if we need this for SW cur-
     sor it depends on which level the sw cursor is drawn)

RAC_COLORMAP

     for colormap operations

RAC_VIEWPORT

     for the call to ChipAdjustFrame()

The flags are ORed together.

10.  Config file ``Option'' entries

Option entries are permitted in most sections and subsections of the config
file.  There are two forms of option entries:

      Option "option-name"
            A boolean option.

      Option "option-name" "option-value"
            An option with an arbitrary value.

The option entries are handled by the parser, and a list of the parsed
options is included with each of the appropriate data structures that the
drivers have access to.  The data structures used to hold the option informa-
tion are opaque to the driver, and a driver must not access the option data
directly.  Instead, the common layer provides a set of functions that may be
used to access, check and manipulate the option data.

First, the low level option handling functions.  In most cases drivers would
not need to use these directly.

     pointer xf86FindOption(pointer options, const char *name)

          Takes a list of options and an option name, and returns a
          handle for the first option entry in the list matching
          the name.  Returns NULL if no match is found.
     char *xf86FindOptionValue(pointer options, const char *name)

          Takes a list of options and an option name, and returns
          the value associated with the first option entry in the
          list matching the name.  If the matching option has no
          value, an empty string ("") is returned.  Returns NULL if
          no match is found.

     void xf86MarkOptionUsed(pointer option)

          Takes a handle for an option, and marks that option as
          used.

     void xf86MarkOptionUsedByName(pointer options, const char *name)

          Takes a list of options and an option name and marks the
          first option entry in the list matching the name as used.

Next, the higher level functions that most drivers would use.

     void xf86CollectOptions(ScrnInfoPtr pScrn, pointer extraOpts)

          Collect the options from each of the config file sections
          used by the screen (pScrn) and return the merged list as
          pScrn->options.  This function requires that pScrn->conf-
          Screen, pScrn->display, pScrn->monitor, pScrn->numEnti-
          ties, and pScrn->entityList are initialised.  extraOpts
          may optionally be set to an additional list of options to
          be combined with the others.  The order of precedence for
          options is extraOpts, display, confScreen, monitor,
          device.

     void xf86ProcessOptions(int scrnIndex, pointer options,

               OptionInfoPtr optinfo)

          Processes a list of options according to the information
          in the array of OptionInfoRecs (optinfo).  The resulting
          information is stored in the value fields of the appro-
          priate optinfo entries.  The found fields are set to TRUE
          when an option with a value of the correct type if found,
          and FALSE otherwise.  The type field is used to determine
          the expected value type for each option.  Each option in
          the list of options for which there is a name match (but
          not necessarily a value type match) is marked as used.
          Warning messages are printed when option values don't
          match the types specified in the optinfo data.

          NOTE: If this function is called before a driver's screen
          number is known (e.g., from the ChipProbe() function) a
          scrnIndex value of -1 should be used.

          The OptionInfoRec is defined as follows:

                       typedef struct {
                           double freq;
                           int units;
                       } OptFrequency;

                       typedef union {
                           unsigned long       num;
                           char *              str;
                           double              realnum;
                           Bool                bool;
                           OptFrequency        freq;
                       } ValueUnion;

                       typedef enum {
                           OPTV_NONE = 0,
                           OPTV_INTEGER,
                           OPTV_STRING,     /* a non-empty string */
                           OPTV_ANYSTR,     /* Any string, including an empty one */
                           OPTV_REAL,
                           OPTV_BOOLEAN,
                           OPTV_FREQ
                       } OptionValueType;

                       typedef enum {
                           OPTUNITS_HZ = 1,
                           OPTUNITS_KHZ,
                           OPTUNITS_MHZ
                       } OptFreqUnits;

                       typedef struct {
                           int                 token;
                           const char*         name;
                           OptionValueType     type;
                           ValueUnion          value;
                           Bool                found;
                       } OptionInfoRec, *OptionInfoPtr;

          OPTV_FREQ can be used for options values that are fre-
          quencies.  These values are a floating point number with
          an optional unit name appended.  The unit name can be one
          of "Hz", "kHz", "k", "MHz", "M".  The multiplier associ-
          ated with the unit is stored in freq.units, and the
          scaled frequency is stored in freq.freq.  When no unit is
          specified, freq.units is set to 0, and freq.freq is
          unscaled.

          Typical usage is to setup a static array of OptionIn-
          foRecs with the token, name, and type fields initialised.
          The value and found fields get set by xf86ProcessOp-
          tions().  For cases where the value parsing is more com-
          plex, the driver should specify OPTV_STRING, and parse
          the string itself.  An example of using this option han-
          dling is included in the Sample Driver (section 20., page
          1) section.

     void xf86ShowUnusedOptions(int scrnIndex, pointer options)

          Prints out warning messages for each option in the list
          of options that isn't marked as used.  This is intended
          to show options that the driver hasn't recognised.  It
          would normally be called near the end of the Chip-
          ScreenInit() function, but only when
          serverGeneration == 1.

     OptionInfoPtr xf86TokenToOptinfo(OptionInfoPtr table, int token)

          Returns a pointer to the OptionInfoRec in table with a
          token field matching token.  Returns NULL if no match is
          found.

     Bool xf86IsOptionSet(OptionInfoPtr table, int token)

          Returns the found field of the OptionInfoRec in table
          with a token field matching token.  This can be used for
          options of all types.  Note that for options of type
          OPTV_BOOLEAN, it isn't sufficient to check this to deter-
          mine the value of the option.  Returns FALSE if no match
          is found.

     char *xf86GetOptValString(OptionInfoPtr table, int token)

          Returns the value.str field of the OptionInfoRec in table
          with a token field matching token.  Returns NULL if no
          match is found.

     Bool xf86GetOptValInteger(OptionInfoPtr table, int token,

               int *value)

          Returns via *value the value.num field of the OptionIn-
          foRec in table with a token field matching token.  *value
          is only changed when a match is found so it can be safely
          initialised with a default prior to calling this func-
          tion.  The function return value is as for xf86IsOption-
          Set().

     Bool xf86GetOptValULong(OptionInfoPtr table, int token,

               unsigned long *value)

          Like xf86GetOptValInteger(), except the value is treated
          as an unsigned long.

     Bool xf86GetOptValReal(OptionInfoPtr table, int token,

               double *value)

          Like xf86GetOptValInteger(), except that value.realnum is
          used.

     Bool xf86GetOptValFreq(OptionInfoPtr table, int token,

               OptFreqUnits expectedUnits, double *value)

          Like xf86GetOptValInteger(), except that the value.freq
          data is returned.  The frequency value is scaled to the
          units indicated by expectedUnits.  The scaling is exact
          when the units were specified explicitly in the option's
          value.  Otherwise, the expectedUnits field is used as a
          hint when doing the scaling.  In this case, values larger
          than 1000 are assumed to have be specified in the next
          smallest units.  For example, if the Option value is
          "10000" and expectedUnits is OPTUNITS_MHZ, the value
          returned is 10.

     Bool xf86GetOptValBool(OptionInfoPtr table, int token, Bool *value)

          This function is used to check boolean options
          (OPTV_BOOLEAN).  If the function return value is FALSE,
          it means the option wasn't set.  Otherwise *value is set
          to the boolean value indicated by the option's value.  No
          option value is interpreted as TRUE.  Option values mean-
          ing TRUE are "1", "yes", "on", "true", and option values
          meaning FALSE are "0", "no", "off", "false".  Option
          names both with the "no" prefix in their names, and with
          that prefix removed are also checked and handled in the
          obvious way.  *value is not changed when the option isn't
          present.  It should normally be set to a default value
          before calling this function.

     Bool xf86ReturnOptValBool(OptionInfoPtr table, int token, Bool def)

          This function is used to check boolean options
          (OPTV_BOOLEAN).  If the option is set, its value is
          returned.  If the options is not set, the default value
          specified by def is returned.  The option interpretation
          is the same as for xf86GetOptValBool().

     int xf86NameCmp(const char *s1, const char *s2)

          This function should be used when comparing strings from
          the config file with expected values.  It works like str-
          cmp(), but is not case sensitive and space, tab, and `_'
          characters are ignored in the comparison.  The use of
          this function isn't restricted to parsing option values.
          It may be used anywhere where this functionality
          required.

11.  Modules, Drivers, Include Files and Interface Issues

NOTE: this section is incomplete.

11.1  Include files

The following include files are typically required by video drivers:

     All drivers should include these:

          "xf86.h"

          "xf86_OSproc.h"

          "xf86_ansic.h"

          "xf86Resources.h"

     Wherever inb/outb (and related things) are used the following
     should be included:

          "compiler.h"

     Drivers that need to access PCI vendor/device definitions need
     this:

          "xf86PciInfo.h"

     Drivers that need to access the PCI config space need this:

          "xf86Pci.h"

     Drivers that initialise a SW cursor need this:

          "mipointer.h"

     All drivers implementing backing store need this:

          "mibstore.h"

     All drivers using the mi colourmap code need this:

          "micmap.h"

     If a driver uses the vgahw module, it needs this:

          "vgaHW.h"

     Drivers supporting VGA or Hercules monochrome screens need:

          "xf1bpp.h"

     Drivers supporting VGA or EGC 16-colour screens need:

          "xf4bpp.h"

     Drivers using cfb need:

          #define PSZ 8

          #include "cfb.h"

          #undef PSZ

     Drivers supporting bpp 16, 24 or 32 with cfb need one or more of:

          "cfb16.h"

          "cfb24.h"

          "cfb32.h"

     If a driver uses XAA, it needs these:

          "xaa.h"

          "xaalocal.h"

     If a driver uses the fb manager, it needs this:

          "xf86fbman.h"

Non-driver modules should include "xf86_ansic.h" to get the correct wrapping
of ANSI C/libc functions.

All modules must NOT include any system include files, or the following:

     "xf86Priv.h"

     "xf86Privstr.h"

     "xf86_libc.h"

     "xf86_OSlib.h"

     "Xos.h"

or any other include files with ``priv'' in their name.

12.  Offscreen Memory Manager

Management of offscreen video memory may be handled by the XFree86 frame-
buffer manager.  Once the offscreen memory manager is running, drivers or
extensions may allocate, free or resize areas of offscreen video memory using
the following functions (definitions taken from xf86fbman.h):

         typedef struct _FBArea {
             ScreenPtr    pScreen;
             BoxRec       box;
             int          granularity;
             void         (*MoveAreaCallback)(struct _FBArea*, struct _FBArea*)
             void         (*RemoveAreaCallback)(struct _FBArea*)
             DevUnion     devPrivate;
         } FBArea, *FBAreaPtr;

         typedef void (*MoveAreaCallbackProcPtr)(FBAreaPtr from, FBAreaPtr to)
         typedef void (*RemoveAreaCallbackProcPtr)(FBAreaPtr)

         FBAreaPtr xf86AllocateOffscreenArea (
             ScreenPtr pScreen,
             int width, int height,
             int granularity,
             MoveAreaCallbackProcPtr MoveAreaCallback,
             RemoveAreaCallbackProcPtr RemoveAreaCallback,
             pointer privData
         )

         void xf86FreeOffscreenArea (FBAreaPtr area)

         Bool xf86ResizeOffscreenArea (
          FBAreaPtr area
          int w, int h
         )

The function:

     Bool xf86FBManagerRunning(ScreenPtr pScreen)

can be used by an extension to check if the driver has initialized the memory
manager.  The manager is not available if this returns FALSE and the func-
tions above will all fail.

xf86AllocateOffscreenArea() can be used to request a rectangle of dimensions
width x height (in pixels) from unused offscreen memory.  granularity speci-
fies that the leftmost edge of the rectangle must lie on some multiple of
granularity pixels.  A granularity of zero means the same thing as a granu-
larity of one - no alignment preference.  A MoveAreaCallback can be provided
to notify the requester when the offscreen area is moved.  If no MoveArea-
Callback is supplied then the area is considered to be immovable.  The priv-
Data field will be stored in the manager's internal structure for that allo-
cated area and will be returned to the requester in the FBArea passed via the
MoveAreaCallback.  An optional RemoveAreaCallback is provided.  If the driver
provides this it indicates that the area should be allocated with a lower
priority.  Such an area may be removed when a higher priority request (one
that doesn't have a RemoveAreaCallback) is made.  When this function is
called, the driver will have an opportunity to do whatever cleanup it needs
to do to deal with the loss of the area, but it must finish its cleanup
before the function exits since the offscreen memory manager will free the
area immediately after.

xf86AllocateOffscreenArea() returns NULL if it was unable to allocate the
requested area.  When no longer needed, areas should be freed with xf86Free-
OffscreenArea().

xf86ResizeOffscreenArea() resizes an existing FBArea.  xf86ResizeOff-
screenArea() returns TRUE if the resize was successful.  If xf86ResizeOff-
screenArea() returns FALSE, the original FBArea is left unmodified.  Resizing
an area maintains the area's original granularity, devPrivate, and MoveArea-
Callback.  xf86ResizeOffscreenArea() has considerably less overhead than
freeing the old area then reallocating the new size, so it should be used
whenever possible.

The function:

     Bool xf86QueryLargestOffscreenArea(

               ScreenPtr pScreen,

               int *width, int *height,

               int granularity,

               int preferences,

               int priority

     )

is provided to query the width and height of the largest single FBArea allo-
catable given a particular priority.  preferences can be one of the following
to indicate whether width, height or area should be considered when determin-
ing which is the largest single FBArea available.

     FAVOR_AREA_THEN_WIDTH

     FAVOR_AREA_THEN_HEIGHT

     FAVOR_WIDTH_THEN_AREA

     FAVOR_HEIGHT_THEN_AREA

priority is one of the following:

     PRIORITY_LOW

          Return the largest block available without stealing any-
          one else's space.  This corresponds to the priority of
          allocating a FBArea when a RemoveAreaCallback is pro-
          vided.

     PRIORITY_NORMAL

          Return the largest block available if it is acceptable to
          steal a lower priority area from someone.  This corre-
          sponds to the priority of allocating a FBArea without
          providing a RemoveAreaCallback.

     PRIORITY_EXTREME

          Return the largest block available if all FBAreas that
          aren't locked down were expunged from memory first.  This
          corresponds to any allocation made directly after a call
          to xf86PurgeUnlockedOffscreenAreas().

The function:

     Bool xf86PurgeUnlockedOffscreenAreas(ScreenPtr pScreen)

is provided as an extreme method to free up offscreen memory.  This will
remove all removable FBArea allocations.

Initialization of the XFree86 framebuffer manager is done via

     Bool xf86InitFBManager(ScreenPtr pScreen,  BoxPtr FullBox)

FullBox represents the area of the framebuffer that the manager is allowed to
manage.  This is typically a box with a width of pScrn->displayWidth and a
height of as many lines as can be fit within the total video memory, however,
the driver can reserve areas at the extremities by passing a smaller area to
the manager.

xf86InitFBManager() must be called before XAA is initialized since XAA uses
the manager for it's pixmap cache.

An alternative function is provided to allow the driver to initialize the
framebuffer manager with a Region rather than a box.

     Bool xf86InitFBManagerRegion(ScreenPtr pScreen,

               RegionPtr FullRegion)

xf86InitFBManagerRegion(), unlike xf86InitFBManager(), does not remove the
area used for the visible screen so that area should not be included in the
region passed to the function.  xf86InitFBManagerRegion() is useful when non-
contiguous areas are available to be managed, and is required when multiple
framebuffers are stored in video memory (as in the case where an overlay of a
different depth is stored as a second framebuffer in offscreen memory).

13.  Colormap Handling

A generic colormap handling layer is provided within the XFree86 common
layer.  This layer takes care of most of the details, and only requires a
function from the driver that loads the hardware palette when required.  To
use the colormap layer, a driver calls the xf86HandleColormaps() function.

     Bool xf86HandleColormaps(ScreenPtr pScreen, int maxColors,

               int sigRGBbits, LoadPaletteFuncPtr loadPalette,

               SetOverscanFuncPtr setOverscan, unsigned int flags)

          This function must be called after the default colormap
          has been initialised.  The pScrn->gamma field must also
          be initialised, preferably by calling xf86SetGamma().
          maxColors is the number of entries in the palette.
          sigRGBbits is the number of significant bits in each
          colour component.  This would normally be the same as
          pScrn->rgbBits.  loadPalette is a driver-provided func-
          tion for loading a colormap into the hardware, and is
          described below.  setOverscan is an optional function
          that may be provided when the overscan color is an index
          from the standard LUT and when it needs to be adjusted to
          keep it as close to black as possible.  The setOverscan
          function programs the overscan index.  It shouldn't nor-
          mally be used for depths other than 8.  setOverscan
          should be set to NULL when it isn't needed.  flags may be
          set to the following (which may be ORed together):

          CMAP_PALETTED_TRUECOLOR

               the TrueColor visual is paletted and is just a
               special case of DirectColor.  This flag is only
               valid for bpp > 8.

          CMAP_RELOAD_ON_MODE_SWITCH

               reload the colormap automatically after mode
               switches.  This is useful for when the driver
               is resetting the hardware during mode switches
               and corrupting or erasing the hardware palette.

          CMAP_LOAD_EVEN_IF_OFFSCREEN

               reload the colormap even if the screen is
               switched out of the server's VC.  The palette
               is not reloaded when the screen is switched
               back in, nor after mode switches.  This is use-
               ful when the driver needs to keep track of
               palette changes.

          The colormap layer normally reloads the palette after VT
          enters so it is not necessary for the driver to save and
          restore the palette when switching VTs.  The driver must,
          however, still save the initial palette during server
          start up and restore it during server exit.

     void LoadPalette(ScrnInfoPtr pScrn, int numColors, int *indices,

               LOCO *colors, VisualPtr pVisual)

          LoadPalette() is a driver-provide function for loading a
          colormap into hardware.  colors is the array of RGB val-
          ues that represent the full colormap.  indices is a list
          of index values into the colors array.  These indices
          indicate the entries that need to be updated.  numColors
          is the number of the indices to be updated.

     void SetOverscan(ScrnInfoPtr pScrn, int overscan)

          SetOverscan() is a driver-provided function for program-
          ming the overscan index.  As described above, it is nor-
          mally only appropriate for LUT modes where all colormap
          entries are available for the display, but where one of
          them is also used for the overscan (typically 8bpp for
          VGA compatible LUTs).  It isn't required in cases where
          the overscan area is never visible.

14.  DPMS Extension

Support code for the DPMS extension is included in the XFree86 common layer.
This code provides an interface between the main extension code, and a means
for drivers to initialise DPMS when they support it.  One function is avail-
able to drivers to do this initialisation, and it is always available, even
when the DPMS extension is not supported by the core server (in which case it
returns a failure result).

     Bool xf86DPMSInit(ScreenPtr pScreen, DPMSSetProcPtr set, int flags)

          This function registers a driver's DPMS level programming
          function set.  It also checks pScrn->options for the
          "dpms" option, and when present marks DPMS as being
          enabled for that screen.  The set function is called
          whenever the DPMS level changes, and is used to program
          the requested level.  flags is currently not used, and
          should be 0.  If the initialisation fails for any reason,
          including when there is no DPMS support in the core
          server, the function returns FALSE.

Drivers that implement DPMS support must provide the following function, that
gets called when the DPMS level is changed:

     void ChipDPMSSet(ScrnInfoPtr pScrn, int level, int flags)

          Program the DPMS level specified by level.  Valid values
          of level are DPMSModeOn, DPMSModeStandby, DPMSModeSus-
          pend, DPMSModeOff.  These values are defined in "exten-
          sions/dpms.h".

15.  DGA Extension

Drivers can support the XFree86 Direct Graphics Architecture (DGA) by filling
out a structure of function pointers and a list of modes and passing them to
DGAInit.

     Bool DGAInit(ScreenPtr pScreen, DGAFunctionPtr funcs,

               DGAModePtr modes, int num)

               /** The DGAModeRec **/

               typedef struct {
                 int num;
                 DisplayModePtr mode;
                 int flags;
                 int imageWidth;
                 int imageHeight;
                 int pixmapWidth;
                 int pixmapHeight;
                 int bytesPerScanline;
                 int byteOrder;
                 int depth;
                 int bitsPerPixel;
                 unsigned long red_mask;
                 unsigned long green_mask;
                 unsigned long blue_mask;
                 int viewportWidth;
                 int viewportHeight;
                 int xViewportStep;
                 int yViewportStep;
                 int maxViewportX;
                 int maxViewportY;
                 int viewportFlags;
                 int offset;
                 unsigned char *address;
                 int reserved1;
                 int reserved2;
               } DGAModeRec, *DGAModePtr;

          num

               Can be ignored.  The DGA DDX will assign these
               numbers.

          mode

               A pointer to the DisplayModeRec for this mode.

          flags

               The following flags are defined and may be OR'd
               together:

               DGA_CONCURRENT_ACCESS

                    Indicates that the driver supports
                    concurrent graphics accelerator and
                    linear framebuffer access.

               DGA_FILL_RECT

               DGA_BLIT_RECT

               DGA_BLIT_RECT_TRANS

                    Indicates that the driver supports
                    the FillRect, BlitRect or BlitTran-
                    sRect functions in this mode.

               DGA_PIXMAP_AVAILABLE

                    Indicates that Xlib may be used on
                    the framebuffer.  This flag will usu-
                    ally be set unless the driver wishes
                    to prohibit this for some reason.

               DGA_INTERLACED

               DGA_DOUBLESCAN

                    Indicates that these are interlaced
                    or double scan modes.

          imageWidth

          imageHeight

               These are the dimensions of the linear frame-
               buffer accessible by the client.

          pixmapWidth

          pixmapHeight

               These are the dimensions of the area of the
               framebuffer accessible by the graphics acceler-
               ator.

          bytesPerScanline

               Pitch of the framebuffer in bytes.

          byteOrder

               Usually the same as pScrn->imageByteOrder.

          depth

               The depth of the framebuffer in this mode.

          bitsPerPixel

               The number of bits per pixel in this mode.

          red_mask

          green_mask

          blue_mask

               The RGB masks for this mode, if applicable.

          viewportWidth

          viewportHeight

               Dimensions of the visible part of the frame-
               buffer.  Usually mode->HDisplay and mode->VDis-
               play.

          xViewportStep

          yViewportStep

               The granularity of x and y viewport positions
               that the driver supports in this mode.

          maxViewportX

          maxViewportY

               The maximum viewport position supported by the
               driver in this mode.

          viewportFlags

               The following may be OR'd together:

               DGA_FLIP_IMMEDIATE

                    The driver supports immediate view-
                    port changes.

               DGA_FLIP_RETRACE

                    The driver supports viewport changes
                    at retrace.

          offset

               The offset into the linear framebuffer that
               corresponds to pixel (0,0) for this mode.

               /** The DGAFunctionRec **/

               typedef struct {
                 Bool (*OpenFramebuffer)(
                      ScrnInfoPtr pScrn,
                      char **name,
                      unsigned char **mem,
                      int *size,
                      int *offset,
                      int *extra
                 );
                 void (*CloseFramebuffer)(ScrnInfoPtr pScrn);
                 Bool (*SetMode)(ScrnInfoPtr pScrn, DGAModePtr pMode);
                 void (*SetViewport)(ScrnInfoPtr pScrn, int x, int y, int flags);
                 int  (*GetViewport)(ScrnInfoPtr pScrn);
                 void (*Flush)(ScrnInfoPtr);
                 void (*FillRect)(
                      ScrnInfoPtr pScrn,
                      int x, int y, int w, int h,
                      unsigned long color
                 );
                 void (*BlitRect)(
                      ScrnInfoPtr pScrn,
                      int srcx, int srcy,
                      int w, int h,
                      int dstx, int dsty
                 );
                 void (*BlitTransRect)(
                      ScrnInfoPtr pScrn,
                      int srcx, int srcy,
                      int w, int h,
                      int dstx, int dsty,
                      unsigned long color
                 );
               } DGAFunctionRec, *DGAFunctionPtr;

     Bool OpenFramebuffer (pScrn, name, mem, size, offset, extra)

          OpenFramebuffer() should pass the client everything it
          needs to know to be able to open the framebuffer.  These
          parameters are OS specific and their meanings are to be
          interpreted by an OS specific client library.

          name

               The name of the device to open or NULL if there
               is no special device to open.  A NULL name
               tells the client that it should open whatever
               device one would usually open to access physi-
               cal memory.

          mem

               The physical address of the start of the frame-
               buffer.

          size

               The size of the framebuffer in bytes.

          offset

               Any offset into the device, if applicable.

          flags

               Any additional information that the client may
               need.  Currently, only the DGA_NEED_ROOT flag
               is defined.

     void CloseFramebuffer (pScrn)

          CloseFramebuffer() merely informs the driver (if it even
          cares) that client no longer needs to access the frame-
          buffer directly.  This function is optional.

     Bool SetMode (pScrn, pMode)

          SetMode() tells the driver to initialize the mode passed
          to it.  If pMode is NULL, then the driver should restore
          the original pre-DGA mode.

     void SetViewport (pScrn, x, y, flags)

          SetViewport() tells the driver to make the upper left-
          hand corner of the visible screen correspond to coordi-
          nate (x,y) on the framebuffer.  Flags currently defined
          are:

          DGA_FLIP_IMMEDIATE

               The viewport change should occur immediately.

          DGA_FLIP_RETRACE

               The viewport change should occur at the verti-
               cal retrace, but this function should return
               sooner if possible.

          The (x,y) locations will be passed as the client speci-
          fied them, however, the driver is expected to round these
          locations down to the next supported location as speci-
          fied by the xViewportStep and yViewportStep for the cur-
          rent mode.

     int GetViewport (pScrn)

          GetViewport() gets the current page flip status.  Set
          bits in the returned int correspond to viewport change
          requests still pending.  For instance, set bit zero if
          the last SetViewport request is still pending, bit one if
          the one before that is still pending, etc.

     void Flush (pScrn)

          This function should ensure that any graphics accelerator
          operations have finished.  This function should not
          return until the graphics accelerator is idle.

     void FillRect (pScrn, x, y, w, h, color)

          This optional function should fill a rectangle w × h
          located at (x,y) in the given color.

     void BlitRect (pScrn, srcx, srcy, w, h, dstx, dsty)

          This optional function should copy an area w × h located
          at (srcx,srcy) to location (dstx,dsty).  This function
          will need to handle copy directions as appropriate.

     void BlitTransRect (pScrn, srcx, srcy, w, h, dstx, dsty, color)

          This optional function is the same as BlitRect except
          that pixels in the source corresponding to the color key
          color should be skipped.

16.  The XFree86 X Video Extension (Xv) Device Dependent Layer

XFree86 offers the X Video Extension which allows clients to treat video as
any another primitive and ``Put'' video into drawables.  By default, the
extension reports no video adaptors as being available since the DDX layer
has not been initialized.  The driver can initialize the DDX layer by filling
out one or more XF86VideoAdaptorRecs as described later in this document and
passing a list of XF86VideoAdaptorPtr pointers to the following function:

     Bool xf86XVScreenInit(

               ScreenPtr pScreen,
               XF86VideoAdaptorPtr *adaptPtrs,

               int num)

After doing this, the extension will report video adaptors as being avail-
able, providing the data in their respective XF86VideoAdaptorRecs was valid.
xf86XVScreenInit() copies data from the structure passed to it so the driver
may free it after the initialization.  At the moment, the DDX only supports
rendering into Window drawables.  Pixmap rendering will be supported after a
sufficient survey of suitable hardware is completed.

The XF86VideoAdaptorRec:

          typedef struct {
               unsigned char type;
               int flags;
               char *name;
               int nEncodings;
               XF86VideoEncodingPtr pEncodings;
               int nFormats;
               XF86VideoFormatPtr pFormats;
               int nPorts;
               XF86AttributeListPtr pAttributes;
               DevUnion *pPortPrivates;
               PutVideoFuncPtr PutVideo;
               PutStillFuncPtr PutStill;
               GetVideoFuncPtr GetVideo;
               GetStillFuncPtr GetStill;
               StopVideoFuncPtr StopVideo;
               SetPortAttributeFuncPtr SetPortAttribute;
               GetPortAttributeFuncPtr GetPortAttribute;
               QueryBestSizeFuncPtr QueryBestSize;
          } XF86VideoAdaptorRec, *XF86VideoAdaptorPtr;

     Each adaptor will have its own XF86VideoAdaptorRec.  The fields are
     as follows:

     type

          This can be XvInputMask, XvOutputMask or both OR'd
          together.  This refers to the target drawable and is sim-
          ilar to a Window's class.  XvInputMask indicates that the
          adaptor can put video into a drawable.  XvOutputMask
          indicates that the adaptor can get video from a drawable.

     flags

          Currently, the following flags are defined:

          VIDEO_NO_CLIPPING

               This indicates that the video adaptor does not
               support clipping.  The driver will never
               receive Get/Put requests where less than the
               entire area determined by drw_x, drw_y, drw_w
               and drw_h is visible.

          VIDEO_INVERT_CLIPLIST

               This indicates that the video driver requires
               the clip list to contain the regions which are
               obscured rather than the regions which are are
               visible.

          VIDEO_EXPOSE

               This flag applies to GetStill and GetVideo
               only, it indicates the clip list shall contain
               obscured regions.  Note the source region will
               still be clipped against the screen bounds.
               This flag is meant for showing all the contents
               of the [root] window, if the administrator has
               no hesitations regarding security.

          VIDEO_OVERLAID_STILLS

               Implementing PutStill for hardware that does
               video as an overlay can be awkward since it's
               unclear how long to leave the video up for.
               When this flag is set, StopVideo will be called
               whenever the destination gets clipped or moved
               so that the still can be left up until then.

     name

          The name of the adaptor.

     nEncodings

     pEncodings

          The number of encodings the adaptor is capable of and
          pointer to the XF86VideoEncodingRec array.  The
          XF86VideoEncodingRec is described later on.

     nFormats

     pFormats

          The number of formats the adaptor is capable of and
          pointer to the XF86VideoFormatRec array.  The XF86Video-
          FormatRec is described later on.

     nPorts

     pPortPrivates

          The number of ports is the number of separate data
          streams which the adaptor can handle simultaneously.  If
          you have more than one port, the adaptor is expected to
          be able to render into more than one window at a time.
          pPortPrivates is an array of pointers or ints - one for
          each port.  A port's private data will be passed to the
          driver any time the port is requested to do something
          like put the video or stop the video.  In the case where
          there may be many ports, this enables the driver to know
          which port the request is intended for.  Most commonly,
          this will contain a pointer to the data structure con-
          taining information about the port.

     pAttributes

          There is an array of XF86AttributeListRecs with an entry
          for each port.

     PutVideo PutStill GetVideo GetStill StopVideo SetPortAttribute Get-
     PortAttribute QueryBestSize

          These functions define the DDX->driver interface.  In
          each case, the pointer data is passed to the driver.
          This is the port private for that port as described
          above.  All fields are required except under the follow-
          ing conditions:

            1.  PutVideo and PutStill are not required when the
                adaptor type does not contain XvInputMask.

            2.  GetVideo and GetStill are not required when the
                adaptor type does not contain XvOutputMask.

          These functions should return Success if the operation
          was completed successfully.  They can return XvBadAlloc
          otherwise.  Xv DDX will not call a Get/Put function while
          video is active, rather issue a StopVideo call first.

          Earlier versions of Xv DDX had a ReclipVideo function,
          obsolete now.  The clip region will be passed directly by
          the functions below.  If the VIDEO_NO_CLIPPING flag is
          set, the RegionPtr should be ignored by the driver.
          ClipBoxes is an X-Y banded region identical to those used
          throughout the server.  The clipBoxes represent the visi-
          ble portions of area determined by drw_x, drw_y, drw_w
          and drw_h in the Get/Put function.  The boxes are in
          screen coordinates, are guaranteed not to overlap and an
          empty region will be passed only to GetVideo, once.  This
          to notify the driver the primitive is totally obscured
          now.  A StopVideo call will immediately follow neverthe-
          less.  In the case where the VIDEO_INVERT_CLIPLIST flag
          is set, clipBoxes will indicate the areas of the primi-
          tive which are obscured rather than the areas visible.
          The Region must not be altered by the driver and will be
          deleted when the function returns.

     typedef  int (* PutVideoFuncPtr)( ScrnInfoPtr pScrn,
               short vid_x, short vid_y, short drw_x, short drw_y,

               short vid_w, short vid_h, short drw_w, short drw_h,

               RegionPtr clipBoxes, pointer data )

          This indicates that the driver should take a subsection
          vid_w × vid_h at location (vid_x,vid_y) from the video
          stream and direct it into the rectangle rw_w × drw_h at
          location (drw_x,drw_y) on the screen, scaling as neces-
          sary.  Due to the large variations in capabilities of the
          various hardware expected to be used with this extension,
          it is not expected that all hardware will be able to do
          this exactly as described.  In that case the driver
          should just do ``the best it can,'' scaling as closely to
          the target rectangle as it can without rendering outside
          of it.  In the worst case, the driver can opt to just not
          turn on the video.

     typedef  int (* PutStillFuncPtr)( ScrnInfoPtr pScrn,
               short vid_x, short vid_y, short drw_x, short drw_y,

               short vid_w, short vid_h, short drw_w, short drw_h,

               RegionPtr clipBoxes, pointer data )

          This is same as PutVideo except that the driver should
          place only one frame from the stream on the screen.

     typedef int (* GetVideoFuncPtr)( ScrnInfoPtr pScrn,
               short vid_x, short vid_y, short drw_x, short drw_y,

               short vid_w, short vid_h, short drw_w, short drw_h,

               RegionPtr clipBoxes, pointer data )

          This is same as PutVideo except that the driver gets
          video from the screen and outputs it.  The driver should
          do the best it can to get the requested dimensions cor-
          rect without reading from an area larger than requested.

     typedef int (* GetStillFuncPtr)( ScrnInfoPtr pScrn,
               short vid_x, short vid_y, short drw_x, short drw_y,

               short vid_w, short vid_h, short drw_w, short drw_h,

               RegionPtr clipBoxes, pointer data )

          This is the same as GetVideo except that the driver
          should place only one frame from the screen into the out-
          put stream.

     typedef void (* StopVideoFuncPtr)(ScrnInfoPtr pScrn,
               pointer data, Bool cleanup)

          This indicates the the driver should stop displaying the
          video.  This is used to stop both input and output video.
          The cleanup field indicates that the video is being
          stopped because the client requested it to stop or
          because the server is exiting the current VT.  In that
          case the driver should deallocate any offscreen memory
          areas (if there are any) being used to put the video to
          the screen.  If cleanup is not set, the video is being
          stopped temporarily due to clipping or moving of the win-
          dow, etc...  and video will likely be restarted soon so
          the driver should not deallocate any offscreen areas
          associated with that port.

     typedef int (* SetPortAttributeFuncPtr)(ScrnInfoPtr pScrn,

               Atom attribute,INT32 value, pointer data)

     typedef int (* GetPortAttributeFuncPtr)(ScrnInfoPtr pScrn,
               Atom attribute,INT32 *value, pointer data)

          A port may have particular attributes such as hue, satu-
          ration, brightness or contrast.  Xv clients set and get
          these attribute values by sending attribute strings
          (Atoms) to the server.  Such requests end up at these
          driver functions.  It is recommended that the driver pro-
          vide at least the following attributes mentioned in the
          Xv client library docs:

               XV_ENCODING

               XV_HUE

               XV_SATURATION

               XV_BRIGHTNESS

               XV_CONTRAST

          but the driver may recognize as many atoms as it wishes.
          If a requested attribute is unknown by the driver it
          should return BadMatch.  XV_ENCODING is the attribute
          intended to let the client specify which video encoding
          the particular port should be using (see the description
          of XF86VideoEncodingRec below).  If the requested encod-
          ing is unsupported, the driver should return XvBadEncod-
          ing.  Success should be returned otherwise.

     typedef void (* QueryBestSizeFuncPtr)(ScrnInfoPtr pScrn,

               Bool motion, short vid_w, short vid_h,

               short drw_w, short drw_h,
               unsigned int *p_w, unsigned int *p_h, pointer data)

          QueryBestSize provides the client with a way to query
          what the destination dimensions would end up being if
          they were to request that an area vid_w × vid_h from the
          video stream be scaled to rectangle of drw_w × drw_h on
          the screen.  Since it is not expected that all hardware
          will be able to get the target dimensions exactly, it is
          important that the driver provide this function.  The
          returned dimensions must be less than or equal to the
          requested dimension.

The XF86VideoEncodingRec:

          typedef struct {
               int id;
               char *name;
               unsigned short width, height;
               XvRationalRec rate;
          } XF86VideoEncodingRec, *XF86VideoEncodingPtr;
     The XF86VideoEncodingRec specifies what encodings the adaptor can
     support.  Most of this data is just informational and for the
     client's benefit, and is what will be reported by XvQueryEncodings.
     The id field is expected to be a unique identifier to allow the
     client to request a certain encoding via the XV_ENCODING attribute
     string.

The XF86VideoFormatRec:

          typedef struct {
               char  depth;
               short class;
          } XF86VideoFormatRec, *XF86VideoFormatPtr;

     This specifies what visuals the video is viewable in.  depth is the
     depth of the visual (not bpp).  class is the visual class such as
     TrueColor, DirectColor or PseudoColor.  Initialization of an adap-
     tor will fail if none of the visuals on that screen are supported.

The XF86AttributeListRec:

          typedef struct {
               int   number;
               int   *flags;
               char  **names;
          } XF86AttributeListRec, *XF86AttributeListPtr;

     Each port will have one of these indicating the number of
     attributes for that port, an array of names of the attributes and
     an array of flags associated with each attribute.  Both arrays are
     number in size.  Currently defined flags are XvGettable and XvSet-
     table which may be OR'd together indicating that attribute is
     ``gettable'' or ``settable'' by the client.  Both arrays can be
     nulled if number is zero.  While the Xv DDX copies most data from
     these structures and stores it internally, including adaptor and
     encoding names, the attribute names are not copied, but only their
     pointers.  Because of this, the strings pointed to by names[] must
     exist as long as Xv is initialized.

17.  The Loader

This section describes the interfaces to the module loader.  The loader
interfaces can be divided into two groups: those that are only available to
the XFree86 common layer, and those that are also available to modules.

17.1  Loader Overview

The loader is capable of loading modules in a range of object formats, and
knowledge of these formats is built in to the loader.  Knowledge of new
object formats can be added to the loader in a straightforward manner.  This
makes it possible to provide OS-independent modules (for a given CPU archi-
tecture type).  In addition to this, the loader can load modules via the OS-
provided dlopen(3) service where available.  Such modules are not platform
independent, and the semantics of dlopen() on most systems results in signif-
icant limitations in the use of modules of this type.  Support for dlopen()
modules in the loader is primarily for experimental and development purposes.

Symbols exported by the loader (on behalf of the core X server) to modules
are determined at compile time.  Only those symbols explicitly exported are
available to modules.  All external symbols of loaded modules are exported to
other modules, and to the core X server.  The loader can be requested to
check for unresolved symbols at any time, and the action to be taken for
unresolved symbols can be controlled by the caller of the loader.  Typically
the caller identifies which symbols can safely remain unresolved and which
cannot.

17.2  Semi-private Loader Interface

The following is the semi-private loader interface that is available to the
XFree86 common layer.

     void LoaderInit(void)

          The LoaderInit() function initialises the loader, and it
          must be called once before calling any other loader func-
          tions.  This function initialises the tables of exported
          symbols, and anything else that might need to be ini-
          tialised.

     void LoaderSetPath(const char *path)

          The LoaderSetPath() function initialises a default module
          search path.  This must be called if calls to other func-
          tions are to be made without explicitly specifying a mod-
          ule search path.  The search path path must be a string
          of one or more comma separated absolute paths.  Modules
          are expected to be located below these paths, possibly in
          subdirectories of these paths.

     pointer LoadModule(const char *module, const char *path,

               const char **subdirlist, const char **patternlist,

               pointer options, const XF86ModReqInfo * modreq,

               int *errmaj, int *errmin)

          The LoadModule() function loads the module called module.
          The return value is a module handle, and may be used in
          future calls to the loader that require a reference to a
          loaded module.  The module name module is normally the
          module's canonical name, which doesn't contain any direc-
          tory path information, or any object/library file pre-
          fixes of suffixes.  Currently a full pathname and/or
          filename is also accepted.  This might change.  The other
          parameters are:

          path

               An optional comma-separated list of module
               search paths.  When NULL, the default search
               path is used.

          subdirlist

               An optional NULL terminated list of subdirecto-
               ries to search.  When NULL, the default built-
               in list is used (refer to stdSubdirs in load-
               mod.c).  The default list is also substituted
               for entries in subdirlist with the value
               DEFAULT_LIST.  This makes is possible to aug-
               ment the default list instead of replacing it.
               Subdir elements must be relative, and must not
               contain "..".  If any violate this requirement,
               the load fails.

          patternlist

               An optional NULL terminated list of POSIX regu-
               lar expressions used to connect module file-
               names with canonical module names.  Each regex
               should contain exactly one subexpression that
               corresponds to the canonical module name.  When
               NULL, the default built-in list is used (refer
               to stdPatterns in loadmod.c).  The default list
               is also substituted for entries in patternlist
               with the value DEFAULT_LIST.  This makes it
               possible to augment the default list instead of
               replacing it.

          options

               An optional parameter that is passed to the
               newly loaded module's SetupProc function (if it
               has one).  This argument is normally a NULL
               terminated list of Options, and must be inter-
               preted that way by modules loaded directly by
               the XFree86 common layer.  However, it may be
               used for application-specific parameter passing
               in other situations.

               When loading ``external'' modules (modules that
               don't have the the standard entry point, for
               example a special shared library) the options
               parameter can be set to EXTERN_MODULE to tell
               the loader not to reject the module when it
               doesn't find the standard entry point.

          modreq

               An optional XF86ModReqInfo* containing ver-
               sion/ABI/vendor information to requirements to
               check the newly loaded module against.  The
               main purpose of this is to allow the loader to
               verify that a module of the correct type/ver-
               sion before running its SetupProc function.
               The XF86ModReqInfo struct is defined as fol-
               lows:

                    typedef struct {
                         CARD8        majorversion;  /* MAJOR_UNSPEC */
                         CARD8        minorversion;  /* MINOR_UNSPEC */
                         CARD16       patchlevel;    /* PATCH_UNSPEC */
                         const char * abiclass;      /* ABI_CLASS_NONE */
                         CARD32       abiversion;    /* ABI_VERS_UNSPEC */
                         const char * moduleclass;   /* MOD_CLASS_NONE */
                    } XF86ModReqInfo;

               The information here is compared against the
               equivalent information in the module's XF86Mod-
               uleVersionInfo record (which is described
               below).  The values in comments above indicate
               ``don't care'' settings for each of the fields.
               The comparisons made are as follows:

               majorversion

                    Must match the module's majorversion
                    exactly.

               minorversion

                    The module's minor version must be no
                    less than this value.  This compari-
                    son is only made if majorversion is
                    specified and matches.

               patchlevel

                    The module's patchlevel must be no
                    less than this value.  This compari-
                    son is only made if minorversion is
                    specified and matches.

               abiclass

                    String must match the module's abi-
                    class string.

               abiversion

                    Must be consistent with the module's
                    abiversion (major equal, minor no
                    older).

               moduleclass

                    String must match the module's mod-
                    uleclass string.

          errmaj

               An optional pointer to a variable holding the
               major part or the error code.  When provided,
               it *errmaj is filled in when LoadModule()
               fails.

          errmin

               Like errmaj, but for the minor part of the
               error code.

     void UnloadModule(pointer mod)

          This function unloads the module referred to by the han-
          dle mod.  All child modules are also unloaded recur-
          sively.  This function must not be used to directly
          unload modules that are child modules (i.e., those that
          have been loaded with LoadSubModule()).

17.3  Module Requirements

Modules must provide information about themselves to the loader, and may
optionally provide entry points for "setup" and "teardown" functions (those
two functions are referred to here as SetupProc and TearDownProc).

The module information is contained in the XF86ModuleVersionInfo struct,
which is defined as follows:

          typedef struct {
              const char * modname;      /* name of module, e.g. "foo" */
              const char * vendor;       /* vendor specific string */
              CARD32       _modinfo1_;   /* constant MODINFOSTRING1/2 to find */
              CARD32       _modinfo2_;   /* infoarea with a binary editor/sign tool */
              CARD32       xf86version;  /* contains XF86_VERSION_CURRENT */
              CARD8        majorversion; /* module-specific major version */
              CARD8        minorversion; /* module-specific minor version */
              CARD16       patchlevel;   /* module-specific patch level */
              const char * abiclass;     /* ABI class that the module uses */
              CARD32       abiversion;   /* ABI version */
              const char * moduleclass;  /* module class */
              CARD32       checksum[4];  /* contains a digital signature of the */
                                         /* version info structure */
          } XF86ModuleVersionInfo;

     The fields are used as follows:

     modname

          The module's name.  This field is currently only for
          informational purposes, but the loader may be modified in
          future to require it to match the module's canonical
          name.

     vendor

          The module vendor.  This field is for informational pur-
          poses only.

     _modinfo1_

          This field holds the first part of a signature that can
          be used to locate this structure in the binary.  It
          should always be initialised to MODINFOSTRING1.

     _modinfo2_

          This field holds the second part of a signature that can
          be used to locate this structure in the binary.  It
          should always be initialised to MODINFOSTRING2.

     xf86version

          The XFree86 version against which the module was com-
          piled.  This is mostly for informational/diagnostic pur-
          poses.  It should be initialised to XF86_VERSION_CURRENT,
          which is defined in xf86Version.h.

     majorversion

          The module-specific major version.  For modules where
          this version is used for more than simply informational
          purposes, the major version should only change (be incre-
          mented) when ABI incompatibilities are introduced, or ABI
          components are removed.

     minorversion

          The module-specific minor version.  For modules where
          this version is used for more than simply informational
          purposes, the minor version should only change (be incre-
          mented) when ABI additions are made in a backward compat-
          ible way.  It should be reset to zero when the major ver-
          sion is increased.

     patchlevel

          The module-specific patch level.  The patch level should
          increase with new revisions of the module where there are
          no ABI changes, and it should be reset to zero when the
          minor version is increased.

     abiclass

          The ABI class that the module requires.  The class is
          specified as a string for easy extensibility.  It should
          indicate which (if any) of the X server's built-in ABI
          classes that the module relies on, or a third-party ABI
          if appropriate.  Built-in ABI classes currently defined
          are:
               ABI_CLASS_NONE
                    no class

               ABI_CLASS_ANSIC

                    only requires the ANSI C interfaces

               ABI_CLASS_VIDEODRV

                    requires the video driver ABI

               ABI_CLASS_XINPUT

                    requires the XInput driver ABI

               ABI_CLASS_EXTENSION

                    requires the extension module ABI

               ABI_CLASS_FONT

                    requires the font module ABI

     abiversion

          The version of abiclass that the module requires.  The
          version consists of major and minor components.  The
          major version must match and the minor version must be no
          newer than that provided by the server or parent module.
          Version identifiers for the built-in classes currently
          defined are:
               ABI_ANSIC_VERSION

               ABI_VIDEODRV_VERSION

               ABI_XINPUT_VERSION

               ABI_EXTENSION_VERSION

               ABI_FONT_VERSION

     moduleclass

          This is similar to the abiclass field, except that it
          defines the type of module rather than the ABI it
          requires.  For example, although all video drivers
          require the video driver ABI, not all modules that
          require the video driver ABI are video drivers.  This
          distinction can be made with the moduleclass.  Currently
          pre-defined module classes are:

               MOD_CLASS_NONE

               MOD_CLASS_VIDEODRV

               MOD_CLASS_XINPUT

               MOD_CLASS_FONT

               MOD_CLASS_EXTENSION

     checksum

          Not currently used.

The module version information, and the optional SetupProc and TearDownProc
entry points are found by the loader by locating a data object in the module
called "modnameModuleData", where "modname" is the canonical name of the mod-
ule.  Modules must contain such a data object, and it must be declared with
global scope, be compile-time initialised, and is of the following type:

          typedef struct {
              XF86ModuleVersionInfo *     vers;
              ModuleSetupProc             setup;
              ModuleTearDownProc          teardown;
          } XF86ModuleData;

The vers parameter must be initialised to a pointer to a correctly ini-
tialised XF86ModuleVersionInfo struct.  The other two parameter are optional,
and should be initialised to NULL when not required.  The other parameters
are defined as

     typedef pointer (*ModuleSetupProc)(pointer, pointer, int *, int *)

     typedef void (*ModuleTearDownProc)(pointer)

     pointer SetupProc(pointer module, pointer options,

               int *errmaj, int *errmin)

          When defined, this function is called by the loader after
          successfully loading a module.  module is a handle for
          the newly loaded module, and maybe used by the SetupProc
          if it calls other loader functions that require a refer-
          ence to it.   The remaining arguments are those that were
          passed to the LoadModule() (or LoadSubModule()), and are
          described above.  When the SetupProc is successful it
          must return a non-NULL value.  The loader checks this,
          and if it is NULL it unloads the module and reports the
          failure to the caller of LoadModule().  If the SetupProc
          does things that need to be undone when the module is
          unloaded, it should define a TearDownProc, and return a
          pointer that the TearDownProc can use to undo what has
          been done.

          When a module is loaded multiple times, the SetupProc is
          called once for each time it is loaded.

     void TearDownProc(pointer tearDownData)

          When defined, this function is called when the loader
          unloads a module.  The tearDownData parameter is the
          return value of the SetupProc() that was called when the
          module was loaded.  The purpose of this function is to
          clean up before the module is unloaded (for example, by
          freeing allocated resources).

17.4  Public Loader Interface

The following is the Loader interface that is available to any part of the
server, and may also be used from within modules.

     pointer LoadSubModule(pointer parent, const char *module,

               const char **subdirlist, const char **patternlist,

               pointer options, const XF86ModReqInfo * modreq,

               int *errmaj, int *errmin)

          This function is like the LoadModule() function described
          above, except that the module loaded is registered as a
          child of the calling module.  The parent parameter is the
          calling module's handle.  Modules loaded with this func-
          tion are automatically unloaded when the parent module is
          unloaded.  The other difference is that the path parame-
          ter may not be specified.  The module search path used
          for modules loaded with this function is the default
          search path as initialised with LoaderSetPath().

     void UnloadSubModule(pointer module)

          This function unloads the module with handle module.  If
          that module itself has children, they are also unloaded.
          It is like LoadModule(), except that it is safe to use
          for unloading child modules.

     pointer LoaderSymbol(const char *symbol)

          This function returns the address of the symbol with name
          symbol.  This may be used to locate a module entry point
          with a known name.

     char **LoaderlistDirs(const char **subdirlist,

               const char **patternlist)

          This function returns a NULL terminated list of canonical
          modules names for modules found in the default module
          search path.  The subdirlist and patternlist parameters
          are as described above, and can be used to control the
          locations and names that are searched.  If no modules are
          found, the return value is NULL.  The returned list
          should be freed by calling LoaderFreeDirList() when it is
          no longer needed.

     void LoaderFreeDirList(char **list)

          This function frees a module list created by Loaderlist-
          Dirs().

     void LoaderReqSymLists(const char **list0, ...)

          This function allows the registration of required symbols
          with the loader.  It is normally used by a caller of
          LoadSubModule().  If any symbols registered in this way
          are found to be unresolved when LoaderCheckUnresolved()
          is called then LoaderCheckUnresolved() will report a
          failure.  The function takes one or more NULL terminated
          lists of symbols.  The end of the argument list is indi-
          cated by a NULL argument.

     void LoaderReqSymbols(const char *sym0, ...)

          This function is like LoaderReqSymLists() except that its
          arguments are symbols rather than lists of symbols.  This
          function is more convenient when single functions are to
          be registered, especially when the single function might
          depend on runtime factors.  The end of the argument list
          is indicated by a NULL argument.

     void LoaderRefSymLists(const char **list0, ...)

          This function allows the registration of possibly unre-
          solved symbols with the loader.  When LoaderCheckUnre-
          solved() is run it won't generate warnings for symbols
          registered in this way unless they were also registered
          as required symbols.

     void LoaderRefSymbols(const char *sym0, ...)

          This function is like LoaderRefSymLists() except that its
          arguments are symbols rather than lists of symbols.  This
          function is more convenient when single functions are to
          be registered, especially when the single function might
          depend on runtime factors.  The end of the argument list
          is indicated by a NULL argument.

     int LoaderCheckUnresolved(int delayflag)

          This function checks for unresolved symbols.  It gener-
          ates warnings for unresolved symbols that have not been
          registered with LoaderRefSymLists(), and maps them to a
          dummy function.  This behaviour may change in future.  If
          unresolved symbols are found that have been registered
          with LoaderReqSymLists() or LoaderReqSymbols() then this
          function returns a non-zero value.  If none of these sym-
          bols are unresolved the return value is zero, indicating
          success.

          The delayflag parameter should normally be set to
          LD_RESOLV_IFDONE.

     LoaderErrorMsg(const char *name, const char *modname,

               int errmaj, int errmin)

          This function prints an error message that includes the
          text ``Failed to load module'', the module name modname,
          a message specific to the errmaj value, and the value if
          errmin.  If name is non-NULL, it is printed as an identi-
          fying prefix to the message (followed by a `:').

17.5  Special Registration Functions

The loader contains some functions for registering some classes of modules.
These may be moved out of the loader at some point.

     void LoadExtension(ExtensionModule *ext)

          This registers the entry points for the extension identi-
          fied by ext.  The ExtensionModule struct is defined as:

                    typedef struct {
                        InitExtension       initFunc;
                        char *              name;
                        Bool                *disablePtr;
                        InitExtension       setupFunc;
                    } ExtensionModule;

     void LoadFont(FontModule *font)

          This registers the entry points for the font rasteriser
          module identified by font.  The FontModule struct is
          defined as:

                    typedef struct {
                        InitFont    initFunc;
                        char *      name;
                        pointer     module;
                    } FontModule;

18.  Helper Functions

This section describe ``helper'' functions that video driver might find use-
ful.  While video drivers are not required to use any of these to be consid-
ered ``compliant'', the use of appropriate helpers is strongly encouraged to
improve the consistency of driver behaviour.

18.1  Functions for printing messages

     ErrorF(const char *format, ...)

          This is the basic function for writing to the error log
          (typically stderr and/or a log file).  Video drivers
          should usually avoid using this directly in favour of the
          more specialised functions described below.  This func-
          tion is useful for printing messages while debugging a
          driver.

     FatalError(const char *format, ...)

          This prints a message and causes the Xserver to abort.
          It should rarely be used within a video driver, as most
          error conditions should be flagged by the return values
          of the driver functions.  This allows the higher layers
          to decide how to proceed.  In rare cases, this can be
          used within a driver if a fatal unexpected condition is
          found.

     xf86ErrorF(const char *format, ...)

          This is like ErrorF(), except that the message is only
          printed when the Xserver's verbosity level is set to the
          default (1) or higher.  It means that the messages are
          not printed when the server is started with the -quiet
          flag.  Typically this function would only be used for
          continuing messages started with one of the more spe-
          cialised functions described below.

     xf86ErrorFVerb(int verb, const char *format, ...)

          Like xf86ErrorF(), except the minimum verbosity level for
          which the message is to be printed is given explicitly.
          Passing a verb value of zero means the message is always
          printed.  A value higher than 1 can be used for informa-
          tion would normally not be needed, but which might be
          useful when diagnosing problems.

     xf86Msg(MessageType type, const char *format, ...)

          This is like xf86ErrorF(), except that the message is
          prefixed with a marker determined by the value of type.
          The marker is used to indicate the type of message (warn-
          ing, error, probed value, config value, etc).  Note the
          xf86Verbose value is ignored for messages of type
          X_ERROR.

          The marker values are:

               X_PROBED

                    Value was probed.

               X_CONFIG

                    Value was given in the config file.

               X_DEFAULT

                    Value is a default.

               X_CMDLINE

                    Value was given on the command line.

               X_NOTICE

                    Notice.

               X_ERROR

                    Error message.

               X_WARNING

                    Warning message.

               X_INFO

                    Informational message.

               X_NONE

                    No prefix.

     xf86MsgVerb(MessageType type, int verb, const char *format, ...)

          Like xf86Msg(), but with the verbosity level given
          explicitly.

     xf86DrvMsg(int scrnIndex, MessageType type, const char *format,
     ...)

          This is like xf86Msg() except that the driver's name (the
          name field of the ScrnInfoRec) followed by the scrnIndex
          in parentheses is printed following the prefix.  This
          should be used by video drivers in most cases as it
          clearly indicates which driver/screen the message is for.
          If scrnIndex is negative, this function behaves exactly
          like xf86Msg().
          NOTE: This function can only be used after the ScrnIn-
          foRec and its name field have been allocated.  That means
          that it can not be used before the END of the ChipProbe()
          function.  Prior to that, use xf86Msg(), providing the
          driver's name explicitly.  No screen number can be sup-
          plied at that point.

     xf86DrvMsgVerb(int scrnIndex, MessageType type, int verb,

               const char *format, ...)

          Like xf86DrvMsg(), but with the verbosity level given
          explicitly.

18.2  Functions for setting values based on command line and config file

     Bool xf86SetDepthBpp(ScrnInfoPtr scrp, int depth, int bpp,

               int fbbpp, int depth24flags)

          This function sets the depth, pixmapBPP and bitsPerPixel
          fields of the ScrnInfoRec.  It also determines the
          defaults for display-wide attributes and pixmap formats
          the screen will support, and finds the Display subsection
          that matches the depth/bpp.  This function should nor-
          mally be called very early from the ChipPreInit() func-
          tion.
          It requires that the confScreen field of the ScrnInfoRec
          be initialised prior to calling it.  This is done by the
          XFree86 common layer prior to calling ChipPreInit().

          The parameters passed are:

          depth

               driver's preferred default depth if no other is
               given.  If zero, use the overall server
               default.

          bpp

               Same, but for the pixmap bpp.

          fbbpp

               Same, but for the framebuffer bpp.

          depth24flags

               Flags that indicate the level of 24/32bpp sup-
               port and whether conversion between different
               framebuffer and pixmap formats is supported.
               The flags for this argument are defined as fol-
               lows, and multiple flags may be ORed together:

               NoDepth24Support
                    No depth 24 formats supported

               Support24bppFb

                    24bpp framebuffer supported

               Support32bppFb

                    32bpp framebuffer supported

               SupportConvert24to32

                    Can convert 24bpp pixmap to 32bpp fb

               SupportConvert32to24

                    Can convert 32bpp pixmap to 24bpp fb

               ForceConvert24to32

                    Force 24bpp pixmap to 32bpp fb con-
                    version

               ForceConvert32to24

                    Force 32bpp pixmap to 24bpp fb con-
                    version

          It uses the command line, config file, and default values
          in the correct order of precedence to determine the depth
          and bpp values.  It is up to the driver to check the
          results to see that it supports them.  If not the Chip-
          PreInit() function should return FALSE.

          If only one of depth/bpp is given, the other is set to a
          reasonable (and consistent) default.

          If a driver finds that the initial depth24flags it uses
          later results in a fb format that requires more video
          memory than is available it may call this function a sec-
          ond time with a different depth24flags setting.

          On success, the return value is TRUE.  On failure it
          prints an error message and returns FALSE.

          The following fields of the ScrnInfoRec are initialised
          by this function:

               depth, bitsPerPixel, display, imageByteOrder,
               bitmapScanlinePad, bitmapScanlineUnit, bitmap-
               BitOrder, numFormats, formats, fbFormat.

     void xf86PrintDepthBpp(scrnInfoPtr scrp)

          This function can be used to print out the depth and bpp
          settings.  It should be called after the final call to
          xf86SetDepthBpp().

     Bool xf86SetWeight(ScrnInfoPtr scrp, rgb weight, rgb mask)

          This function sets the weight, mask, offset and rgbBits
          fields of the ScrnInfoRec.  It would normally be called
          fairly early in the ChipPreInit() function for
          depths > 8bpp.

          It requires that the depth and display fields of the
          ScrnInfoRec be initialised prior to calling it.
          The parameters passed are:

          weight

               driver's preferred default weight if no other
               is given.  If zero, use the overall server
               default.

          mask

               Same, but for mask.

          It uses the command line, config file, and default values
          in the correct order of precedence to determine the
          weight value.  It derives the mask and offset values from
          the weight and the defaults.  It is up to the driver to
          check the results to see that it supports them.  If not
          the ChipPreInit() function should return FALSE.

          On success, this function prints a message showing the
          weight values selected, and returns TRUE.

          On failure it prints an error message and returns FALSE.

          The following fields of the ScrnInfoRec are initialised
          by this function:

               weight, mask, offset.

     Bool xf86SetDefaultVisual(ScrnInfoPtr scrp, int visual)

          This function sets the defaultVisual field of the ScrnIn-
          foRec.  It would normally be called fairly early from the
          ChipPreInit() function.

          It requires that the depth and display fields of the
          ScrnInfoRec be initialised prior to calling it.

          The parameters passed are:

          visual

               driver's preferred default visual if no other
               is given.  If -1, use the overall server
               default.

          It uses the command line, config file, and default values
          in the correct order of precedence to determine the
          default visual value.  It is up to the driver to check
          the result to see that it supports it.  If not the Chip-
          PreInit() function should return FALSE.

          On success, this function prints a message showing the
          default visual selected, and returns TRUE.

          On failure it prints an error message and returns FALSE.

     Bool xf86SetGamma(ScrnInfoPtr scrp, Gamma gamma)

          This function sets the gamma field of the ScrnInfoRec.
          It would normally be called fairly early from the Chip-
          PreInit() function in cases where the driver supports
          gamma correction.

          It requires that the monitor field of the ScrnInfoRec be
          initialised prior to calling it.
          The parameters passed are:

          gamma

               driver's preferred default gamma if no other is
               given.  If zero (< 0.01), use the overall
               server default.

          It uses the command line, config file, and default values
          in the correct order of precedence to determine the gamma
          value.  It is up to the driver to check the results to
          see that it supports them.  If not the ChipPreInit()
          function should return FALSE.

          On success, this function prints a message showing the
          gamma value selected, and returns TRUE.

          On failure it prints an error message and returns FALSE.

     void xf86SetDpi(ScrnInfoPtr pScrn, int x, int y)

          This function sets the xDpi and yDpi fields of the Scrn-
          InfoRec.  The driver can specify preferred defaults by
          setting x and y to non-zero values.  The -dpi command
          line option overrides all other settings.  Otherwise, if
          the DisplaySize entry is present in the screen's Monitor
          config file section, it is used together with the virtual
          size to calculate the dpi values.  This function should
          be called after all the mode resolution has been done.

     void xf86SetBlackWhitePixels(ScrnInfoPtr pScrn)

          This functions sets the blackPixel and whitePixel fields
          of the ScrnInfoRec according to whether or not the -flip-
          Pixels command line options is present.

     const char *xf86GetVisualName(int visual)

          Returns a printable string with the visual name matching
          the numerical visual class provided.  If the value is
          outside the range of valid visual classes, NULL is
          returned.

18.3  Primary Mode functions

The primary mode helper functions are those which would normally be used by a
driver, unless it has unusual requirements which cannot be catered for the by
the helpers.

     int xf86ValidateModes(ScrnInfoPtr scrp, DisplayModePtr availModes,

               char **modeNames, ClockRangePtr clockRanges,

               int *linePitches, int minPitch, int maxPitch,

               int pitchInc, int minHeight, int maxHeight,

               int virtualX, int virtualY,

               unsigned long apertureSize,

               LookupModeFlags strategy)

          This function basically selects the set of modes to use
          based on those available and the various constraints.  It
          also sets some other related parameters.  It is normally
          called near the end of the ChipPreInit() function.

          The parameters passed to the function are:
          availModes

               List of modes available for the monitor.

          modeNames

               List of mode names that the screen is request-
               ing.

          clockRanges

               A list of clock ranges allowed by the driver.
               Each range includes whether interlaced or mul-
               tiscan modes are supported for that range.  See
               below for more on clockRanges.

          linePitches

               List of supported line pitches supported by the
               driver.  This is optional and should be NULL
               when not used.

          minPitch

               Minimum line pitch supported by the driver.
               This must be supplied when linePitches is NULL,
               and is ignored otherwise.

          maxPitch

               Maximum line pitch supported by the driver.
               This is required when minPitch is required.

          pitchInc

               Granularity of horizontal pitch values as sup-
               ported by the chipset.  This is expressed in
               bits.  This must be supplied.

          minHeight

               minimum virtual height allowed.  If zero, no
               limit is imposed.

          maxHeight

               maximum virtual height allowed.  If zero, no
               limit is imposed.

          virtualX

               If greater than zero, this is the virtual width
               value that will be used.  Otherwise, the vir-
               tual width is chosen to be the smallest that
               can accommodate the modes selected.

          virtualY

               If greater than zero, this is the virtual
               height value that will be used.  Otherwise, the
               virtual height is chosen to be the smallest
               that can accommodate the modes selected.

          apertureSize

               The size (in bytes) of the aperture used to
               access video memory.

          strategy

               The strategy to use when choosing from multiple
               modes with the same name.  The options are:

               LOOKUP_DEFAULT

                    ???

               LOOKUP_BEST_REFRESH

                    mode with best refresh rate

               LOOKUP_CLOSEST_CLOCK

                    mode with closest matching clock

               LOOKUP_LIST_ORDER

                    first usable mode in list

               The following options can also be combined
               (OR'ed) with one of the above:

               LOOKUP_CLKDIV2

                    Allow halved clocks

               LOOKUP_OPTIONAL_TOLERANCES

                    Allow missing horizontal sync and/or
                    vertical refresh ranges in the
                    XF86Config Monitor section

               LOOKUP_OPTIONAL_TOLERANCES should only be spec-
               ified when the driver can ensure all modes it
               generates can sync on, or at least not damage,
               the monitor or digital flat panel.  Horizontal
               sync and/or vertical refresh ranges specified
               by the user will still be honoured (and acted
               upon).

          This function requires that the following fields of the
          ScrnInfoRec are initialised prior to calling it:

          clock[]

               List of discrete clocks (when non-programmable)

          numClocks

               Number of discrete clocks (when non-pro-
               grammable)

          progClock

               Whether the clock is programmable or not

          monitor

               Pointer to the applicable XF86Config monitor
               section

          fdFormat

               Format of the screen buffer

          videoRam

               total video memory size (in bytes)

          maxHValue

               Maximum horizontal timing value allowed

          maxVValue

               Maximum vertical timing value allowed

          xInc

               Horizontal timing increment in pixels (defaults
               to 8)

          This function fills in the following ScrnInfoRec fields:

          modePool

               A subset of the modes available to the monitor
               which are compatible with the driver.

          modes

               One mode entry for each of the requested modes,
               with the status field of each filled in to
               indicate if the mode has been accepted or not.
               This list of modes is a circular list.

          virtualX

               The resulting virtual width.

          virtualY

               The resulting virtual height.

          displayWidth

               The resulting line pitch.

          virtualFrom

               Where the virtual size was determined from.

          The first stage of this function checks that the virtualX
          and virtualY values supplied (if greater than zero) are
          consistent with the line pitch and maxHeight limitations.
          If not, an error message is printed, and the return value
          is -1.

          The second stage sets up the mode pool, eliminating imme-
          diately any modes that exceed the driver's line pitch
          limits, and also the virtual width and height limits (if
          greater than zero).  For each mode removed an informa-
          tional message is printed at verbosity level 2.  If the
          mode pool ends up being empty, a warning message is
          printed, and the return value is 0.

          The final stage is to lookup each mode name, and fill in
          the remaining parameters.  If an error condition is
          encountered, a message is printed, and the return value
          is -1.  Otherwise, the return value is the number of
          valid modes found (0 if none are found).

          Even if the supplied mode names include duplicates, no
          two names will ever match the same mode.  Furthermore, if
          the supplied mode names do not yield a valid mode
          (including the case where no names are passed at all),
          the function will continue looking through the mode pool
          until it finds a mode that survives all checks, or until
          the mode pool is exhausted.

          A message is only printed by this function when a funda-
          mental problem is found.  It is intended that this func-
          tion may be called more than once if there is more than
          one set of constraints that the driver can work within.

          If this function returns -1, the ChipPreInit() function
          should return FALSE.

          clockRanges is a linked list of clock ranges allowed by
          the driver.  If a mode doesn't fit in any of the defined
          clockRanges, it is rejected.  The first clockRange that
          matches all requirements is used.

          clockRanges contains the following fields:

          minClock

          maxClock

               The lower and upper mode clock bounds for which
               the rest of the clockRange parameters apply.
               Since these are the mode clocks, they are not
               scaled with the ClockMulFactor and ClockDivFac-
               tor.  It is up to the driver to adjust these
               values if they depend on the clock scaling fac-
               tors.

          clockIndex

               (not used yet) -1 for programmable clocks

          interlaceAllowed

               TRUE if interlacing is allowed for this range

          doubleScanAllowed

               TRUE if doublescan or multiscan is allowed for
               this range

          ClockMulFactor

          ClockDivFactor

               Scaling factors that are applied to the mode
               clocks ONLY before selecting a clock index
               (when there is no programmable clock) or a Syn-
               thClock value.  This is useful for drivers that
               support pixel multiplexing or that need to
               scale the clocks because of hardware restric-
               tions (like sending 24bpp data to an 8 bit RAM-
               DAC using a tripled clock).

               Note that these parameters describe what must
               be done to the mode clock to achieve the data
               transport clock between graphics controller and
               RAMDAC.  For example for 2:1 pixel multiplex-
               ing, two pixels are sent to the RAMDAC on each
               clock.  This allows the RAMDAC clock to be half
               of the actual pixel clock.  Hence, ClockMulFac-
               tor=1 and ClockDivFactor=2.  This means that
               the clock used for clock selection (ie, deter-
               mining the correct clock index from the list of
               discrete clocks) or for the SynthClock field in
               case of a programmable clock is:  (mode->Clock
               * ClockMulFactor) / ClockDivFactor.

          PrivFlags

               This field is copied into the mode->PrivFlags
               field when this clockRange is selected by
               xf86ValidateModes().  It allows the driver to
               find out what clock range was selected, so it
               knows it needs to set up pixel multiplexing or
               any other range-dependent feature.  This field
               is purely driver-defined: it may contain flag
               bits, an index or anything else (as long as it
               is an INT).

          Note that the mode->SynthClock field is always filled in
          by xf86ValidateModes(): it will contain the ``data trans-
          port clock'', which is the clock that will have to be
          programmed in the chip when it has a programmable clock,
          or the clock that will be picked from the clocks list
          when it is not a programmable one.  Thus:

          mode->SynthClock =

                    (mode->Clock * ClockMulFactor) / ClockDivFactor

     void xf86PruneDriverModes(ScrnInfoPtr scrp)

          This function deletes modes in the modes field of the
          ScrnInfoRec that have been marked as invalid.  This is
          normally run after having run xf86ValidateModes() for the
          last time.  For each mode that is deleted, a warning mes-
          sage is printed out indicating the reason for it being
          deleted.

     void xf86SetCrtcForModes(ScrnInfoPtr scrp, int adjustFlags)

          This function fills in the Crtc* fields for all the modes
          in the modes field of the ScrnInfoRec.  The adjustFlags
          parameter determines how the vertical CRTC values are
          scaled for interlaced modes.  They are halved if it is
          INTERLACE_HALVE_V.  The vertical CRTC values are doubled
          for doublescan modes, and are further multiplied by the
          VScan value.

          This function is normally called after calling
          xf86PruneDriverModes().

     void xf86PrintModes(ScrnInfoPtr scrp)

          This function prints out the virtual size setting, and
          the line pitch being used.  It also prints out one line
          for each mode being used, including its pixel clock, hor-
          izontal sync rate, refresh rate, and whether it is inter-
          laced or multiscan.

          This function is normally called after calling
          xf86SetCrtcForModes().

18.4  Secondary Mode functions

The secondary mode helper functions are functions which are normally used by
the primary mode helper functions, and which are not normally called directly
by a driver.  If a driver has unusual requirements and needs to do its own
mode validation, it might be able to make use of some of these secondary mode
helper functions.

     int xf86GetNearestClock(ScrnInfoPtr scrp, int freq, Bool allowDiv2,

               int *divider)

          This function returns the index of the closest clock to
          the frequency freq given (in kHz).  It assumes that the
          number of clocks is greater than zero.  It requires that
          the numClocks and clock fields of the ScrnInfoRec are
          initialised.  The allowDiv2 field determines if the
          clocks can be halved.  The *divider return value indi-
          cates whether clock division is used when determining the
          clock returned.

          This function is only for non-programmable clocks.

     const char *xf86ModeStatusToString(ModeStatus status)

          This function converts the status value to a descriptive
          printable string.

     ModeStatus xf86LookupMode(ScrnInfoPtr scrp, DisplayModePtr modep,

               ClockRangePtr clockRanges, LookupModeFlags strategy)

          This function takes a pointer to a mode with the name
          filled in, and looks for a mode in the modePool list
          which matches.  The parameters of the matching mode are
          filled in to *modep.  The clockRanges and strategy param-
          eters are as for the xf86ValidateModes() function above.

          This function requires the modePool, clock[], numClocks
          and progClock fields of the ScrnInfoRec to be initialised
          before being called.

          The return value is MODE_OK if a mode was found.  Other-
          wise it indicates why a matching mode could not be found.

     ModeStatus xf86InitialCheckModeForDriver(ScrnInfoPtr scrp,

               DisplayModePtr mode, ClockRangePtr clockRanges,

               LookupModeFlags strategy, int maxPitch,

               int virtualX, int virtualY)

          This function checks the passed mode against some basic
          driver constraints.  Apart from the ones passed explic-
          itly, the maxHValue and maxVValue fields of the ScrnIn-
          foRec are also used.  If the ValidMode field of the Scrn-
          InfoRec is set, that function is also called to check the
          mode.  Next, the mode is checked against the monitor's
          constraints.

          If the mode is consistent with all constraints, the
          return value is MODE_OK.  Otherwise the return value
          indicates which constraint wasn't met.

     void xf86DeleteMode(DisplayModePtr *modeList, DisplayModePtr mode)

          This function deletes the mode given from the modeList.
          It never prints any messages, so it is up to the caller
          to print a message if required.

18.5  Functions for handling strings and tokens

Tables associating strings and numerical tokens combined with the following
functions provide a compact way of handling strings from the config file, and
for converting tokens into printable strings.  The table data structure is:

          typedef struct {
              int                 token;
              const char *        name;
          } SymTabRec, *SymTabPtr;

A table is an initialised array of SymTabRec.  The tokens must be non-nega-
tive integers.  Multiple names may be mapped to a single token.  The table is
terminated with an element with a token value of -1 and NULL for the name.

     const char *xf86TokenToString(SymTabPtr table, int token)

          This function returns the first string in table that
          matches token.  If no match is found, NULL is returned
          (NOTE, older versions of this function would return the
          string "unknown" when no match is found).

     int xf86StringToToken(SymTabPtr table, const char *string)

          This function returns the first token in table that
          matches string.  The xf86NameCmp() function is used to
          determine the match.  If no match is found, -1 is
          returned.

18.6  Functions for finding which config file entries to use

These functions can be used to select the appropriate config file entries
that match the detected hardware.  They are described above in the Probe
(section 5.8, page 1) and Available Functions (section 9.3, page 1) sections.

18.7  Probing discrete clocks on old hardware

The xf86GetClocks() function may be used to assist in finding the discrete
pixel clock values on older hardware.

     void xf86GetClocks(ScrnInfoPtr pScrn, int num,

               Bool (*ClockFunc)(ScrnInfoPtr, int),

               void (*ProtectRegs)(ScrnInfoPtr, Bool),

               void (*BlankScreen)(ScrnInfoPtr, Bool),

               int vertsyncreg, int maskval, int knownclkindex,

               int knownclkvalue)

          This function uses a comparative sampling method to mea-
          sure the discrete pixel clock values.  The number of dis-
          crete clocks to measure is given by num.  clockFunc is a
          function that selects the n'th clock.  It should also
          save or restore any state affected by programming the
          clocks when the index passed is CLK_REG_SAVE or
          CLK_REG_RESTORE.  ProtectRegs is a function that does
          whatever is required to protect the hardware state while
          selecting a new clock.  BlankScreen is a function that
          blanks the screen.  vertsyncreg and maskval are the reg-
          ister and bitmask to check for the presence of vertical
          sync pulses.  knownclkindex and knownclkvalue are the
          index and value of a known clock.  These are the known
          references on which the comparative measurements are
          based.  The number of clocks probed is set in pScrn->num-
          Clocks, and the probed clocks are set in the
          pScrn->clock[] array.  All of the clock values are in
          units of kHz.

     void xf86ShowClocks(ScrnInfoPtr scrp, MessageType from)

          Print out the pixel clocks scrp->clock[].  from indicates
          whether the clocks were probed or from the config file.

19.  The vgahw module

The vgahw modules provides an interface for saving, restoring and programming
the standard VGA registers, and for handling VGA colourmaps.

19.1  Data Structures

The public data structures used by the vgahw module are vgaRegRec and vgaH-
WRec.  They are defined in vgaHW.h.

19.2  General vgahw Functions

     Bool vgaHWGetHWRec(ScrnInfoPtr pScrn)

          This function allocates a vgaHWRec structure, and hooks
          it into the ScrnInfoRec's privates.  Like all information
          hooked into the privates, it is persistent, and only
          needs to be allocated once per screen.  This function
          should normally be called from the driver's ChipPreInit()
          function.  The vgaHWRec is zero-allocated, and the fol-
          lowing fields are explicitly initialised:
          ModeReg.DAC[]

               initialised with a default colourmap

          ModeReg.Attribute[0x11]

               initialised with the default overscan index

          ShowOverscan

               initialised according to the "ShowOverscan"
               option

          paletteEnabled

               initialised to FALSE

          cmapSaved

               initialised to FALSE

          pScrn

               initialised to pScrn

          In addition to the above, vgaHWSetStdFuncs() is called to
          initialise the register access function fields with the
          standard VGA set of functions.

          Once allocated, a pointer to the vgaHWRec can be obtained
          from the ScrnInfoPtr with the VGAHWPTR(pScrn) macro.

     void vgaHWFreeHWRec(ScrnInfoPtr pScrn)

          This function frees a vgaHWRec structure.  It should be
          called from a driver's ChipFreeScreen() function.

     Bool vgaHWSetRegCounts(ScrnInfoPtr pScrn, int numCRTC,

               int numSequencer, int numGraphics, int numAttribute)

          This function allows the number of CRTC, Sequencer,
          Graphics and Attribute registers to be changed.  This
          makes it possible for extended registers to be saved and
          restored with vgaHWSave() and vgaHWRestore().  This func-
          tion should be called after a vgaHWRec has been allocated
          with vgaHWGetHWRec().  The default values are defined in
          vgaHW.h as follows:

                    #define VGA_NUM_CRTC 25
                    #define VGA_NUM_SEQ   5
                    #define VGA_NUM_GFX   9
                    #define VGA_NUM_ATTR 21

     Bool vgaHWCopyReg(vgaRegPtr dst, vgaRegPtr src)

          This function copies the contents of the VGA saved regis-
          ters in src to dst.  Note that it isn't possible to sim-
          ply do this with memcpy() (or similar).  This function
          returns TRUE unless there is a problem allocating space
          for the CRTC and related fields in dst.

     void vgaHWSetStdFuncs(vgaHWPtr hwp)

          This function initialises the register access function
          fields of hwp with the standard VGA set of functions.
          This is called by vgaHWGetHWRec(), so there is usually no
          need to call this explicitly.  The register access func-
          tions are described below.

     void vgaHWSetMmioFuncs(vgaHWPtr hwp, CARD8 *base, int offset)

          This function initialised the register access function
          fields of hwp with a generic MMIO set of functions.
          hwp->MMIOBase is initialised with base, which must be the
          virtual address that the start of MMIO area is mapped to.
          hwp->MMIOOffset is initialised with offset, which must be
          calculated in such a way that when the standard VGA I/O
          port value is added to it the correct offset into the
          MMIO area results.  That means that these functions are
          only suitable when the VGA I/O ports are made available
          in a direct mapping to the MMIO space.  If that is not
          the case, the driver will need to provide its own regis-
          ter access functions.  The register access functions are
          described below.

     Bool vgaHWMapMem(ScrnInfoPtr pScrn)

          This function maps the VGA memory window.  It requires
          that the vgaHWRec be allocated.  If a driver requires
          non-default MapPhys or MapSize settings (the physical
          location and size of the VGA memory window) then those
          fields of the vgaHWRec must be initialised before calling
          this function.  Otherwise, this function initialiases the
          default values of 0xA0000 for MapPhys and (64 * 1024) for
          MapSize.  This function must be called before attempting
          to save or restore the VGA state.  If the driver doesn't
          call it explicitly, the vgaHWSave() and vgaHWRestore()
          functions may call it if they need to access the VGA mem-
          ory (in which case they will also call vgaHWUnmapMem() to
          unmap the VGA memory before exiting).

     void vgaHWUnmapMem(ScrnInfoPtr pScrn)

          This function unmaps the VGA memory window.  It must only
          be called after the memory has been mapped.  The Base
          field of the vgaHWRec field is set to NULL to indicate
          that the memory is no longer mapped.

     void vgaHWGetIOBase(vgaHWPtr hwp)

          This function initialises the IOBase field of the vgaH-
          WRec.  This function must be called before using any
          other functions that access the video hardware.

          A macro VGAHW_GET_IOBASE() is also available in vgaHW.h
          that returns the I/O base, and this may be used when the
          vgahw module is not loaded (for example, in the Chip-
          Probe() function).

     void vgaHWUnlock(vgaHWPtr hwp)

          This function unlocks the VGA CRTC[0-7] registers, and
          must be called before attempting to write to those regis-
          ters.

          A macro VGAHW_UNLOCK(base) is also available in vgaHW.h
          that does the same thing, and this may be used when the
          vgahw module is not loaded (for example, in the Chip-
          Probe() function).

     void vgaHWLock(vgaHWPtr hwp)

          This function locks the VGA CRTC[0-7] registers.

          A macro VGAHW_LOCK(base) is also available in vgaHW.h
          that does the same thing, and this may be used when the
          vgahw module is not loaded (for example, in the Chip-
          Probe() function).

     void vgaHWSave(ScrnInfoPtr pScrn, vgaRegPtr save, int flags)

          This function saves the VGA state.  The state is written
          to the vgaRegRec pointed to by save.  flags is set to one
          or more of the following flags ORed together:

          VGA_SR_MODE

               the mode setting registers are saved

          VGA_SR_FONTS

               the text mode font/text data is saved

          VGA_SR_CMAP

               the colourmap (LUT) is saved

          VGA_SR_ALL

               all of the above are saved

          The vgaHWRec and its IOBase fields must be initialised
          before this function is called.  If VGA_SR_FONTS is set
          in flags, the VGA memory window must be mapped.  If it
          isn't then vgaHWMapMem() will be called to map it, and
          vgaHWUnmapMem() will be called to unmap it afterwards.
          vgaHWSave() uses the three functions below in the order
          vgaHWSaveColormap(), vgaHWSaveMode(), vgaHWSaveFonts() to
          carry out the different save phases.  It is undecided at
          this stage whether they will be part of the vgahw mod-
          ule's public interface or not.

     void vgaHWSaveMode(ScrnInfoPtr pScrn, vgaRegPtr save)

          This functions saves the VGA mode registers.  They are
          saved to the vgaRegRec pointed to by save.  The registers
          saved are:

               MiscOut

               CRTC[0-0x18]

               Attribute[0-0x14]

               Graphics[0-8]

               Sequencer[0-4]

     void vgaHWSaveFonts(ScrnInfoPtr pScrn, vgaRegPtr save)

          This functions saves the text mode font and text data
          held in the video memory.  If called while in a graphics
          mode, no save is done.  The VGA memory window must be
          mapped with vgaHWMapMem() before to calling this func-
          tion.

          On some platforms, one or more of the font/text plane
          saves may be no-ops.  This is the case when the plat-
          form's VC driver already takes care of this.

     void vgaHWSaveColormap(ScrnInfoPtr pScrn, vgaRegPtr save)

          This function saves the VGA colourmap (LUT).  Before sav-
          ing it, it attempts to verify that the colourmap is read-
          able.  In rare cases where it isn't readable, a default
          colourmap is saved instead.

     void vgaHWRestore(ScrnInfoPtr pScrn, vgaRegPtr restore, int flags)

          This function programs the VGA state.  The state pro-
          grammed is that contained in the vgaRegRec pointed to by
          restore.  flags is the same as described above for the
          vgaHWSave() function.

          The vgaHWRec and its IOBase fields must be initialised
          before this function is called.  If VGA_SR_FONTS is set
          in flags, the VGA memory window must be mapped.  If it
          isn't then vgaHWMapMem() will be called to map it, and
          vgaHWUnmapMem() will be called to unmap it afterwards.
          vgaHWRestore() uses the three functions below in the
          order vgaHWRestoreFonts(), vgaHWRestoreMode(), vgaHWRe-
          storeColormap() to carry out the different restore
          phases.  It is undecided at this stage whether they will
          be part of the vgahw module's public interface or not.

     void vgaHWRestoreMode(ScrnInfoPtr pScrn, vgaRegPtr restore)

          This functions restores the VGA mode registers.  They are
          restore from the data in the vgaRegRec pointed to by
          restore.  The registers restored are:

               MiscOut

               CRTC[0-0x18]

               Attribute[0-0x14]

               Graphics[0-8]

               Sequencer[0-4]

     void vgaHWRestoreFonts(ScrnInfoPtr pScrn, vgaRegPtr restore)

          This functions restores the text mode font and text data
          to the video memory.  The VGA memory window must be
          mapped with vgaHWMapMem() before to calling this func-
          tion.

          On some platforms, one or more of the font/text plane
          restores may be no-ops.  This is the case when the plat-
          form's VC driver already takes care of this.

     void vgaHWRestoreColormap(ScrnInfoPtr pScrn, vgaRegPtr restore)

          This function restores the VGA colourmap (LUT).

     void vgaHWInit(ScrnInfoPtr pScrn, DisplayModePtr mode)

          This function fills in the vgaHWRec's ModeReg field with
          the values appropriate for programming the given video
          mode.  It requires that the ScrnInfoRec's depth field is
          initialised, which determines how the registers are pro-
          grammed.

     void vgaHWSeqReset(vgaHWPtr hwp, Bool start)

          Do a VGA sequencer reset.  If start is TRUE, the reset is
          started.  If start is FALSE, the reset is ended.

     void vgaHWProtect(ScrnInfoPtr pScrn, Bool on)

          This function protects VGA registers and memory from cor-
          ruption during loads.  It is typically called with on set
          to TRUE before programming, and with on set to FALSE
          after programming.

     Bool vgaHWSaveScreen(ScreenPtr pScreen, Bool on)

          This function blanks and unblanks the screen.  It is
          blanked when on is FALSE, and unblanked when on is TRUE.

     void vgaHWBlankScreen(ScrnInfoPtr pScrn, Bool on)

          This function blanks and unblanks the screen.  It is
          blanked when on is FALSE, and unblanked when on is TRUE.
          This function is provided for use in cases where the
          ScrnInfoRec can't be derived from the ScreenRec, like
          probing for clocks.

19.3  VGA Colormap Functions

The vgahw modules uses the standard colormap support (see the Colormap Han-
dling (section 13., page 1) section.  This is initialised with the following
function:

     Bool vgaHWHandleColormaps(ScreenPtr pScreen)

19.4  VGA Register Access Functions

The vgahw module abstracts access to the standard VGA registers by using a
set of functions held in the vgaHWRec.  When the vgaHWRec is created these
function pointers are initialised with the set of standard VGA I/O register
access functions.  In addition to these, the vgahw module includes a basic
set of MMIO register access functions, and the vgaHWRec function pointers can
be initialised to these by calling the vgaHWSetMmioFuncs() function described
above.  Some drivers/platforms may require a different set of functions for
VGA access.  The access functions are described here.

     void writeCrtc(vgaHWPtr hwp, CARD8 index, CARD8 value)

          Write value to CRTC register index.

     CARD8 readCrtc(vgaHWPtr hwp, CARD8 index)

          Return the value read from CRTC register index.

     void writeGr(vgaHWPtr hwp, CARD8 index, CARD8 value)

          Write value to Graphics Controller register index.

     CARD8 readGR(vgaHWPtr hwp, CARD8 index)

          Return the value read from Graphics Controller register
          index.

     void writeSeq(vgaHWPtr hwp, CARD8 index, CARD8, value)

          Write value to Sequencer register index.

     CARD8 readSeq(vgaHWPtr hwp, CARD8 index)

          Return the value read from Sequencer register index.

     void writeAttr(vgaHWPtr hwp, CARD8 index, CARD8, value)

          Write value to Attribute Controller register index.  When
          writing out the index value this function should set bit
          5 (0x20) according to the setting of hwp->paletteEnabled
          in order to preserve the palette access state.  It should
          be cleared when hwp->paletteEnabled is TRUE and set when
          it is FALSE.

     CARD8 readAttr(vgaHWPtr hwp, CARD8 index)

          Return the value read from Attribute Controller register
          index.  When writing out the index value this function
          should set bit 5 (0x20) according to the setting of
          hwp->paletteEnabled in order to preserve the palette
          access state.  It should be cleared when hwp->paletteEn-
          abled is TRUE and set when it is FALSE.

     void writeMiscOut(vgaHWPtr hwp, CARD8 value)

          Write `value' to the Miscellaneous Output register.

     CARD8 readMiscOut(vgwHWPtr hwp)

          Return the value read from the Miscellaneous Output reg-
          ister.

     void enablePalette(vgaHWPtr hwp)

          Clear the palette address source bit in the Attribute
          Controller index register and set hwp->paletteEnabled to
          TRUE.

     void disablePalette(vgaHWPtr hwp)

          Set the palette address source bit in the Attribute Con-
          troller index register and set hwp->paletteEnabled to
          FALSE.

     void writeDacMask(vgaHWPtr hwp, CARD8 value)

          Write value to the DAC Mask register.

     CARD8 readDacMask(vgaHWptr hwp)

          Return the value read from the DAC Mask register.

     void writeDacReadAddress(vgaHWPtr hwp, CARD8 value)

          Write value to the DAC Read Address register.

     void writeDacWriteAddress(vgaHWPtr hwp, CARD8 value)

          Write value to the DAC Write Address register.

     void writeDacData(vgaHWPtr hwp, CARD8 value)

          Write value to the DAC Data register.

     CARD8 readDacData(vgaHWptr hwp)

          Return the value read from the DAC Data register.

20.  Some notes about writing a driver

NOTE: some parts of this are not up to date

The following is an outline for writing a basic unaccelerated driver for a
PCI video card with a linear mapped framebuffer, and which has a VGA core.
It is includes some general information that is relevant to most drivers
(even those which don't fit that basic description).

The information here is based on the initial conversion of the Matrox Millen-
nium driver to the ``new design''.  For a fleshing out and sample implementa-
tion of some of the bits outlined here, refer to that driver.  Note that this
is an example only.  The approach used here will not be appropriate for all
drivers.

Each driver must reserve a unique driver name, and a string that is used to
prefix all of its externally visible symbols.  This is to avoid name space
clashes when loading multiple drivers.  The examples here are for the ``ZZZ''
driver, which uses the ``ZZZ'' or ``zzz'' prefix for its externally visible
symbols.

20.1  Include files

All drivers normally include the following headers:

     "xf86.h"

     "xf86_OSproc.h"

     "xf86_ansic.h"

     "xf86Resources.h"

Wherever inb/outb (and related things) are used the following should be
included:

     "compiler.h"

Drivers that need to access PCI vendor/device definitions need this:

     "xf86PciInfo.h"

Drivers that need to access the PCI config space need this:

     "xf86Pci.h"

Drivers using the mi banking wrapper need:

     "mibank.h"

Drivers that initialise a SW cursor need this:

     "mipointer.h"

All drivers implementing backing store need this:

     "mibstore.h"

All drivers using the mi colourmap code need this:

     "micmap.h"

If a driver uses the vgahw module, it needs this:

     "vgaHW.h"

Drivers supporting VGA or Hercules monochrome screens need:

     "xf1bpp.h"

Drivers supporting VGA or EGC 16-colour screens need:

     "xf4bpp.h"

Drivers using cfb need:

     #define PSZ 8

     #include "cfb.h"

     #undef PSZ

Drivers supporting bpp 16, 24 or 32 with cfb need one or more of:

     "cfb16.h"

     "cfb24.h"

     "cfb32.h"

The driver's own header file:

     "zzz.h"

Drivers must NOT include the following:

     "xf86Priv.h"

     "xf86Privstr.h"

     "xf86_libc.h"

     "xf86_OSlib.h"

     "Xos.h"

     any OS header

20.2  Data structures and initialisation

   o The following macros should be defined:

          #define VERSION <version-as-an-int>
          #define ZZZ_NAME "ZZZ"         /* the name used to prefix messages */
          #define ZZZ_DRIVER_NAME "zzz"  /* the driver name as used in config file */
          #define ZZZ_MAJOR_VERSION <int>
          #define ZZZ_MINOR_VERSION <int>
          #define ZZZ_PATCHLEVEL    <int>

     XXX Probably want to remove one of these version.

     NOTE: ZZZ_DRIVER_NAME should match the name of the driver module without
     things like the "lib" prefix, the "_drv" suffix or filename extensions.

   o A DriverRec must be defined, which includes the functions required at
     the pre-probe phase.  The name of this DriverRec must be an upper-case
     version of ZZZ_DRIVER_NAME (for the purposes of static linking).

          DriverRec ZZZ = {
              VERSION,
              "unaccelerated driver for ZZZ Zzzzzy cards",
              ZZZIdentify,
              ZZZProbe,
              NULL,
              0
          };

   o Define list of supported chips and their matching ID:

          static SymTabRec ZZZChipsets[] = {
              { PCI_CHIP_ZZZ1234, "zzz1234a" },
              { PCI_CHIP_ZZZ5678, "zzz5678a" },
              { -1,               NULL }
          };

     The token field may be any integer value that the driver may use to
     uniquely identify the supported chipsets.  For drivers that support only
     PCI devices using the PCI device IDs might be a natural choice, but this
     isn't mandatory.  For drivers that support both PCI and other devices
     (like ISA), some other ID should probably used.  When other IDs are used
     as the tokens it is recommended that the names be defined as an enum
     type.

   o If the driver uses the xf86MatchPciInstances() helper (recommended for
     drivers that support PCI cards) a list that maps PCI IDs to chip IDs and
     fixed resources must be defined:

          static PciChipsets ZZZPciChipsets[] = {
              { PCI_CHIP_ZZZ1234, PCI_CHIP_ZZZ1234, RES_SHARED_VGA },
              { PCI_CHIP_ZZZ5678, PCI_CHIP_ZZZ5678, RES_SHARED_VGA },
              { -1,               -1,               RES_UNDEFINED }
          }

   o Define the XF86ModuleVersionInfo struct for the driver.  This is
     required for the dynamically loaded version:

          #ifdef XFree86LOADER
          static XF86ModuleVersionInfo zzzVersRec =
          {
              "zzz",
              MODULEVENDORSTRING,
              MODINFOSTRING1,
              MODINFOSTRING2,
              XF86_VERSION_CURRENT,
              ZZZ_MAJOR_VERSION, ZZZ_MINOR_VERSION, ZZZ_PATCHLEVEL,
              ABI_CLASS_VIDEODRV,
              ABI_VIDEODRV_VERSION,
              MOD_CLASS_VIDEODRV,
              {0,0,0,0}
          };
          #endif

   o Define a data structure to hold the driver's screen-specific data.  This
     must be used instead of global variables.  This would be defined in the
     "zzz.h" file, something like:

          typedef struct {
              type1  field1;
              type2  field2;
              int    fooHack;
              Bool   pciRetry;
              Bool   noAccel;
              Bool   hwCursor;
              CloseScreenProcPtr CloseScreen;
              ...
          } ZZZRec, *ZZZPtr;

   o Define the list of config file Options that the driver accepts.  For
     consistency between drivers those in the list of ``standard'' options
     should be used where appropriate before inventing new options.

          typedef enum {
              OPTION_FOO_HACK,
              OPTION_PCI_RETRY,
              OPTION_HW_CURSOR,
              OPTION_NOACCEL
          } ZZZOpts;

          static OptionInfoRec ZZZOptions[] = {
            { OPTION_FOO_HACK,  "FooHack",   OPTV_INTEGER, {0}, FALSE },
            { OPTION_PCI_RETRY, "PciRetry",  OPTV_BOOLEAN, {0}, FALSE },
            { OPTION_HW_CURSOR, "HWcursor",  OPTV_BOOLEAN, {0}, FALSE },
            { OPTION_NOACCEL,   "NoAccel",   OPTV_BOOLEAN, {0}, FALSE },
            { -1,               NULL,        OPTV_NONE,    {0}, FALSE }
          };

20.3  Functions

20.3.1  SetupProc

For dynamically loaded modules, a ModuleData variable is required.  It is
should be the name of the driver prepended to "ModuleData".  A Setup() func-
tion is also required, which calls xf86AddDriver() to add the driver to the
main list of drivers.

     #ifdef XFree86LOADER

     static MODULESETUPPROTO(mgaSetup);

     XF86ModuleData zzzModuleData = { &zzzVersRec, zzzSetup, NULL };

     static pointer
     zzzSetup(pointer module, pointer opts, int *errmaj, int *errmin)
     {
         static Bool setupDone = FALSE;

         /* This module should be loaded only once, but check to be sure. */

         if (!setupDone) {
             /*
              * Modules that this driver always requires may be loaded
              * here  by calling LoadSubModule().
              */

             setupDone = TRUE;
             xf86AddDriver(&MGA, module, 0);

             /*
              * The return value must be non-NULL on success even though
              * there is no TearDownProc.
              */
             return (pointer)1;
         } else {
             if (errmaj) *errmaj = LDR_ONCEONLY;
             return NULL;
         }
     }
     #endif

20.3.2  GetRec, FreeRec

A function is usually required to allocate the driver's screen-specific data
structure and hook it into the ScrnInfoRec's driverPrivate field.  The Scrn-
InfoRec's driverPrivate is initialised to NULL, so it is easy to check if the
initialisation has already been done.  After allocating it, initialise the
fields.  By using xnfcalloc() to do the allocation it is zeroed, and if the
allocation fails the server exits.

     static Bool
     ZZZGetRec(ScrnInfoPtr pScrn)
     {
         if (pScrn->driverPrivate != NULL)
             return TRUE;
         pScrn->driverPrivate = xnfcalloc(sizeof(ZZZRec), 1);
         /* Initialise as required */
         ...
         return TRUE;
     }

Define a macro in "zzz.h" which gets a pointer to the ZZZRec when given
pScrn:

     #define ZZZPTR(p) ((ZZZPtr)((p)->driverPrivate))

Define a function to free the above, setting it to NULL once it has been
freed:

     static void
     ZZZFreeRec(ScrnInfoPtr pScrn)
     {
         if (pScrn->driverPrivate == NULL)
             return;
         xfree(pScrn->driverPrivate);
         pScrn->driverPrivate = NULL;
     }

20.3.3  Identify

Define the Identify() function.  It is run before the Probe, and typically
prints out an identifying message, which might include the chipsets it sup-
ports.  This function is mandatory:

     static void
     ZZZIdentify(int flags)
     {
         xf86PrintChipsets(ZZZ_NAME, "driver for ZZZ Tech chipsets",
                           ZZZChipsets);
     }

20.3.4  Probe

Define the Probe() function.  The purpose of this is to find all instances of
the hardware that the driver supports, and for the ones not already claimed
by another driver, claim the slot, and allocate a ScrnInfoRec.  This should
be a minimal probe, and it should under no circumstances leave the state of
the hardware changed.  Because a device is found, don't assume that it will
be used.  Don't do any initialisations other than the required ScrnInfoRec
initialisations.  Don't allocate any new data structures.

This function is mandatory.

NOTE: The xf86DrvMsg() functions cannot be used from the Probe.

     static Bool
     ZZZProbe(DriverPtr drv, int flags)
     {
         Bool foundScreen = FALSE;
         int numDevSections, numUsed;
         GDevPtr *devSections;
         int *usedChips;
         int i;

         /*
          * Find the config file Device sections that match this
          * driver, and return if there are none.
          */
         if ((numDevSections = xf86MatchDevice(ZZZ_DRIVER_NAME,
                                               &devSections)) <= 0) {
             return FALSE;
         }

         /*
          * Since this is a PCI card, "probing" just amounts to checking
          * the PCI data that the server has already collected.  If there
          * is none, return.
          *
          * Although the config file is allowed to override things, it
          * is reasonable to not allow it to override the detection
          * of no PCI video cards.
          *
          * The provided xf86MatchPciInstances() helper takes care of
          * the details.
          */
         /* test if PCI bus present */
         if (xf86GetPciVideoInfo()) {

             numUsed = xf86MatchPciInstances(ZZZ_NAME, PCI_VENDOR_ZZZ,
                                 ZZZChipsets, ZZZPciChipsets, devSections,
                                 numDevSections, drv, &usedChips);

             for (i = 0; i < numUsed; i++) {
                 ScrnInfoPtr pScrn;

                 /* Allocate a ScrnInfoRec */
                 pScrn = xf86AllocateScreen(drv, 0);
                 pScrn->driverVersion = VERSION;
                 pScrn->driverName    = ZZZ_DRIVER_NAME;
                 pScrn->name          = ZZZ_NAME;
                 pScrn->Probe         = ZZZProbe;
                 pScrn->PreInit       = ZZZPreInit;
                 pScrn->ScreenInit    = ZZZScreenInit;
                 pScrn->SwitchMode    = ZZZSwitchMode;
                 pScrn->AdjustFrame   = ZZZAdjustFrame;
                 pScrn->EnterVT       = ZZZEnterVT;
                 pScrn->LeaveVT       = ZZZLeaveVT;
                 pScrn->FreeScreen    = ZZZFreeScreen;
                 pScrn->ValidMode     = ZZZValidMode;
                 foundScreen = TRUE;
                 /* add screen to entity */
                 xf86ConfigActivePciEntity(pScrn, usedChips[i],
                             ZZZPciChipsets, NULL, NULL, NULL, NULL, NULL);

             }
             if (numUsed > 0)
                 xfree(usedChips);
         }

     #ifdef HAS_ISA_DEVS
         /*
          * If the driver supports ISA hardware, the following block
          * can be included too.
          */
         numUsed = xf86MatchIsaInstances(ZZZ_NAME, ZZZChipsets,
                                  ZZZIsaChipsets, drv, ZZZFindIsaDevice,
                                  devSections, numDevSections, &usedChips);
         for (i = 0; i < numUsed; i++) {
             ScrnInfoPtr pScrn = xf86AllocateScreen(drv,0);

             pScrn->driverVersion = VERSION;
             pScrn->driverName    = ZZZ_DRIVER_NAME;
             pScrn->name          = ZZZ_NAME;
             pScrn->Probe         = ZZZProbe;
             pScrn->PreInit       = ZZZPreInit;
             pScrn->ScreenInit    = ZZZScreenInit;
             pScrn->SwitchMode    = ZZZSwitchMode;
             pScrn->AdjustFrame   = ZZZAdjustFrame;
             pScrn->EnterVT       = ZZZEnterVT;
             pScrn->LeaveVT       = ZZZLeaveVT;
             pScrn->FreeScreen    = ZZZFreeScreen;
             pScrn->ValidMode     = ZZZValidMode;
             foundScreen = TRUE;
             xf86ConfigActiveIsaEntity(pScrn, usedChips[i], ZZZIsaChipsets,
                                       NULL, NULL, NULL, NULL, NULL);
         }
         if (numUsed > 0)
             xfree(usedChips);
     #endif /* HAS_ISA_DEVS */

         xfree(devSections);
         return foundScreen;

20.3.5  PreInit

Define the PreInit() function.  The purpose of this is to find all the infor-
mation required to determine if the configuration is usable, and to ini-
tialise those parts of the ScrnInfoRec that can be set once at the beginning
of the first server generation.  The information should be found in the least
intrusive way possible.

This function is mandatory.

NOTES:

  1.  The PreInit() function is only called once during the life of the X
      server (at the start of the first generation).

  2.  Data allocated here must be of the type that persists for the life of
      the X server.  This means that data that hooks into the ScrnInfoRec's
      privates field should be allocated here, but data that hooks into the
      ScreenRec's devPrivates field should not be allocated here.  The
      driverPrivate field should also be allocated here.

  3.  Although the ScrnInfoRec has been allocated before this function is
      called, the ScreenRec has not been allocated.  That means that things
      requiring it cannot be used in this function.

  4.  Very little of the ScrnInfoRec has been initialised when this function
      is called.  It is important to get the order of doing things right in
      this function.

     static Bool
     ZZZPreInit(ScrnInfoPtr pScrn, int flags)
     {
         /* Fill in the monitor field */
         pScrn->monitor = pScrn->confScreen->monitor;

         /*
          * If using the vgahw module, it will typically be loaded
          * here by calling xf86LoadSubModule(pScrn, "vgahw");
          */

         /*
          * Set the depth/bpp.  Our preferred default depth/bpp is 8, and
          * we support both 24bpp and 32bpp framebuffer layouts.
          * This sets pScrn->display also.
          */
         if (!xf86SetDepthBpp(pScrn, 8, 8, 8,
                              Support24bppFb | Support32bppFb)) {
             return FALSE;
         } else {
             if (depth/bpp isn't one we support) {
                 print error message;
                 return FALSE;
             }
         }
         /* Print out the depth/bpp that was set */
         xf86PrintDepthBpp(pScrn);

         /* Set bits per RGB for 8bpp */
         if (pScrn->depth <= 8) {
             /* Take into account a dac_6_bit option here */
             pScrn->rgbBits = 6 or 8;
         }

         /*
          * xf86SetWeight() and xf86SetDefaultVisual() must be called
          * after pScrn->display is initialised.
          */

         /* Set weight/mask/offset for depth > 8 */
         if (pScrn->depth > 8) {
             if (!xf86SetWeight(pScrn, defaultWeight, defaultMask)) {
                 return FALSE;
             } else {
                 if (weight isn't one we support) {
                     print error message;
                     return FALSE;
                 }
             }
         }

         /* Set the default visual. */
         if (!xf86SetDefaultVisual(pScrn, -1)) {
             return FALSE;
         } else {
             if (visual isn't one we support) {
                 print error message;
                 return FALSE;
             }
         }

         /* If the driver supports gamma correction, set the gamma. */
         if (!xf86SetGamma(pScrn, default_gamma)) {
             return FALSE;
         }

         /* This driver uses a programmable clock */
         pScrn->progClock = TRUE;

         /* Allocate the ZZZRec driverPrivate */
         if (!ZZZGetRec(pScrn)) {
             return FALSE;
         }

         pZzz = ZZZPTR(pScrn);

         /* Collect all of the option flags (fill in pScrn->options) */
         xf86CollectOptions(pScrn, NULL);

         /*
          * Process the options based on the information in ZZZOptions.
          * The results are written to ZZZOptions.
          */
         xf86ProcessOptions(pScrn->scrnIndex, pScrn->options, ZZZOptions);

         /*
          * Set various fields of ScrnInfoRec and/or ZZZRec based on
          * the options found.
          */
         from = X_DEFAULT;
         pZzz->hwCursor = FALSE;
         if (xf86IsOptionSet(ZZZOptions, OPTION_HW_CURSOR)) {
             from = X_CONFIG;
             pZzz->hwCursor = TRUE;
         }
         xf86DrvMsg(pScrn->scrnIndex, from, "Using %s cursor\n",
                    pZzz->hwCursor ? "HW" : "SW");
         if (xf86IsOptionSet(ZZZOptions, OPTION_NOACCEL)) {
             pZzz->noAccel = TRUE;
             xf86DrvMsg(pScrn->scrnIndex, X_CONFIG,
                        "Acceleration disabled\n");
         } else {
             pZzz->noAccel = FALSE;
         }
         if (xf86IsOptionSet(ZZZOptions, OPTION_PCI_RETRY)) {
             pZzz->UsePCIRetry = TRUE;
             xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "PCI retry enabled\n");
         }
         pZzz->fooHack = 0;
         if (xf86GetOptValInteger(ZZZOptions, OPTION_FOO_HACK,
                                  &pZzz->fooHack)) {
             xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Foo Hack set to %d\n",
                        pZzz->fooHack);
         }

         /*
          * Find the PCI slot(s) that this screen claimed in the probe.
          * In this case, exactly one is expected, so complain otherwise.
          * Note in this case we're not interested in the card types so
          * that parameter is set to NULL.
          */
         if ((i = xf86GetPciInfoForScreen(pScrn->scrnIndex, &pciList, NULL))
             != 1) {
             print error message;
             ZZZFreeRec(pScrn);
             if (i > 0)
                 xfree(pciList);
             return FALSE;
         }
         /* Note that pciList should be freed below when no longer needed */

         /*
          * Determine the chipset, allowing config file chipset and
          * chipid values to override the probed information.  The config
          * chipset value has precedence over its chipid value if both
          * are present.
          *
          * It isn't necessary to fill in pScrn->chipset if the driver
          * keeps track of the chipset in its ZZZRec.
          */

         ...

         /*
          * Determine video memory, fb base address, I/O addresses, etc,
          * allowing the config file to override probed values.
          *
          * Set the appropriate pScrn fields (videoRam is probably the
          * most important one that other code might require), and
          * print out the settings.
          */

         ...

         /* Initialise a clockRanges list. */

         ...

         /* Set any other chipset specific things in the ZZZRec */

         ...

         /* Select valid modes from those available */

         i = xf86ValidateModes(pScrn, pScrn->monitor->Modes,
                               pScrn->display->modes, clockRanges,
                               NULL, minPitch, maxPitch, rounding,
                               minHeight, maxHeight,
                               pScrn->display->virtualX,
                               pScrn->display->virtualY,
                               pScrn->videoRam * 1024,
                               LOOKUP_BEST_REFRESH);
         if (i == -1) {
             ZZZFreeRec(pScrn);
             return FALSE;
         }

         /* Prune the modes marked as invalid */

         xf86PruneDriverModes(pScrn);

         /* If no valid modes, return */

         if (i == 0 || pScrn->modes == NULL) {
             print error message;
             ZZZFreeRec(pScrn);
             return FALSE;
         }

         /*
          * Initialise the CRTC fields for the modes.  This driver expects
          * vertical values to be halved for interlaced modes.
          */
         xf86SetCrtcForModes(pScrn, INTERLACE_HALVE_V);

         /* Set the current mode to the first in the list. */
         pScrn->currentMode = pScrn->modes;

         /* Print the list of modes being used. */
         xf86PrintModes(pScrn);

         /* Set the DPI */
         xf86SetDpi(pScrn, 0, 0);

         /* Load bpp-specific modules */
         switch (pScrn->bitsPerPixel) {
         case 1:
             mod = "xf1bpp";
             break;
         case 4:
             mod = "xf4bpp";
             break;
         case 8:
             mod = "cfb";
             break;
         case 16:
             mod = "cfb16";
             break;
         case 24:
             mod = "cfb24";
             break;
         case 32:
             mod = "cfb32";
             break;
         }
         if (mod && !xf86LoadSubModule(pScrn, mod))
             ZZZFreeRec(pScrn);
             return FALSE;

         /* Load XAA if needed */
         if (!pZzz->noAccel || pZzz->hwCursor)
             if (!xf86LoadSubModule(pScrn, "xaa")) {
                 ZZZFreeRec(pScrn);
                 return FALSE;
             }

         /* Done */
         return TRUE;
     }

20.3.6  MapMem, UnmapMem

Define functions to map and unmap the video memory and any other memory aper-
tures required.  These functions are not mandatory, but it is often useful to
have such functions.

     static Bool
     ZZZMapMem(ScrnInfoPtr pScrn)
     {
         /* Call xf86MapPciMem() to map each PCI memory area */
         ...
         return TRUE or FALSE;
     }

     static Bool
     ZZZUnmapMem(ScrnInfoPtr pScrn)
     {
         /* Call xf86UnMapVidMem() to unmap each memory area */
         ...
         return TRUE or FALSE;
     }

20.3.7  Save, Restore

Define functions to save and restore the original video state.  These func-
tions are not mandatory, but are often useful.

     static void
     ZZZSave(ScrnInfoPtr pScrn)
     {
         /*
          * Save state into per-screen data structures.
          * If using the vgahw module, vgaHWSave will typically be
          * called here.
          */
         ...
     }

     static void
     ZZZRestore(ScrnInfoPtr pScrn)
     {
         /*
          * Restore state from per-screen data structures.
          * If using the vgahw module, vgaHWRestore will typically be
          * called here.
          */
         ...
     }

20.3.8  ModeInit

Define a function to initialise a new video mode.  This function isn't manda-
tory, but is often useful.

     static Bool
     ZZZModeInit(ScrnInfoPtr pScrn, DisplayModePtr mode)
     {
         /*
          * Program a video mode.  If using the vgahw module,
          * vgaHWInit and vgaRestore will typically be called here.
          * Once up to the point where there can't be a failure
          * set pScrn->vtSema to TRUE.
          */
         ...
     }

20.3.9  ScreenInit

Define the ScreenInit() function.  This is called at the start of each server
generation, and should fill in as much of the ScreenRec as possible as well
as any other data that is initialised once per generation.  It should ini-
tialise the framebuffer layers it is using, and initialise the initial video
mode.

This function is mandatory.

NOTE: The ScreenRec (pScreen) is passed to this driver, but it and the Scrn-
InfoRecs are not yet hooked into each other.  This means that in this func-
tion, and functions it calls, one cannot be found from the other.

     static Bool
     ZZZScreenInit(int scrnIndex, ScreenPtr pScreen, int argc, char **argv)
     {
         /* Get the ScrnInfoRec */
         pScrn = xf86Screens[pScreen->myNum];

         /*
          * If using the vgahw module, its data structures and related
          * things are typically initialised/mapped here.
          */

         /* Save the current video state */
         ZZZSave(pScrn);

         /* Initialise the first mode */
         ZZZModeInit(pScrn, pScrn->currentMode);

         /* Set the viewport if supported */

         ZZZAdjustFrame(scrnIndex, pScrn->frameX0, pScrn->frameY0, 0);

         /*
          * Setup the screen's visuals, and initialise the framebuffer
          * code.
          */

         /* Reset the visual list */
         miClearVisualTypes();

         /*
          * Setup the visuals supported.  This driver only supports
          * TrueColor for bpp > 8, so the default set of visuals isn't
          * acceptable.  To deal with this, call miSetVisualTypes with
          * the appropriate visual mask.
          */

         if (pScrn->bitsPerPixel > 8) {
             if (!miSetVisualTypes(pScrn->depth, TrueColorMask,
                                   pScrn->rgbBits, pScrn->defaultVisual))
                 return FALSE;
         } else {
             if (!miSetVisualTypes(pScrn->depth,
                                   miGetDefaultVisualMask(pScrn->depth),
                                   pScrn->rgbBits, pScrn->defaultVisual))
                 return FALSE;
         }

         /*
          * Initialise the framebuffer.
          */

         switch (pScrn->bitsPerPixel) {
         case 1:
             ret = xf1bppScreenInit(pScreen, FbBase,
                                    pScrn->virtualX, pScrn->virtualY,
                                    pScrn->xDpi, pScrn->yDpi,
                                    pScrn->displayWidth);
             break;
         case 4:
             ret = xf4bppScreenInit(pScreen, FbBase,
                                    pScrn->virtualX, pScrn->virtualY,
                                    pScrn->xDpi, pScrn->yDpi,
                                    pScrn->displayWidth);
             break;
         case 8:
             ret = cfbScreenInit(pScreen, FbBase,
                                 pScrn->virtualX, pScrn->virtualY,
                                 pScrn->xDpi, pScrn->yDpi,
                                 pScrn->displayWidth);
             break;
         case 16:
             ret = cfb16ScreenInit(pScreen, FbBase,
                                   pScrn->virtualX, pScrn->virtualY,
                                   pScrn->xDpi, pScrn->yDpi,
                                   pScrn->displayWidth);
             break;
         case 24:
             ret = cfb24ScreenInit(pScreen, FbBase,
                                   pScrn->virtualX, pScrn->virtualY,
                                   pScrn->xDpi, pScrn->yDpi,
                                   pScrn->displayWidth);
             break;
         case 32:
             ret = cfb32ScreenInit(pScreen, FbBase,
                                   pScrn->virtualX, pScrn->virtualY,
                                   pScrn->xDpi, pScrn->yDpi,
                                   pScrn->displayWidth);
             break;
         default:
             print a message about an internal error;
             ret = FALSE;
             break;
         }

         if (!ret)
             return FALSE;

         /* Override the default mask/offset settings */
         if (pScrn->bitsPerPixel > 8) {
             for (i = 0, visual = pScreen->visuals;
                  i < pScreen->numVisuals; i++, visual++) {
                 if ((visual->class | DynamicClass) == DirectColor) {
                     visual->offsetRed = pScrn->offset.red;
                     visual->offsetGreen = pScrn->offset.green;
                     visual->offsetBlue = pScrn->offset.blue;
                     visual->redMask = pScrn->mask.red;
                     visual->greenMask = pScrn->mask.green;
                     visual->blueMask = pScrn->mask.blue;
                 }
             }
         }

         /*
          * If banking is needed, initialise an miBankInfoRec (defined in
          * "mibank.h"), and call miInitializeBanking().
          */
         if (!miInitializeBanking(pScreen, pScrn->virtualX, pScrn->virtualY,
                                          pScrn->displayWidth, pBankInfo))
             return FALSE;

         /*
          * If backing store is to be supported (as is usually the case),
          * initialise it.
          */
         miInitializeBackingStore(pScreen);

         /*
          * Set initial black & white colourmap indices.
          */
         xf86SetBlackWhitePixels(pScreen);

         /*
          * Install colourmap functions.  If using the vgahw module,
          * vgaHandleColormaps would usually be called here.
          */

         ...

         /*
          * Initialise cursor functions.  This example is for the mi
          * software cursor.
          */
         miDCInitialize(pScreen, xf86GetPointerScreenFuncs());

         /* Initialise the default colourmap */
         switch (pScrn->depth) {
         case 1:
             if (!xf1bppCreateDefColormap(pScreen))
                 return FALSE;
             break;
         case 4:
             if (!xf4bppCreateDefColormap(pScreen))
                 return FALSE;
             break;
         default:
             if (!cfbCreateDefColormap(pScreen))
                 return FALSE;
             break;
         }

         /*
          * Wrap the CloseScreen vector and set SaveScreen.
          */
         ZZZPTR(pScrn)->CloseScreen = pScreen->CloseScreen;
         pScreen->CloseScreen = ZZZCloseScreen;
         pScreen->SaveScreen = ZZZSaveScreen;

         /* Report any unused options (only for the first generation) */
         if (serverGeneration == 1) {
             xf86ShowUnusedOptions(pScrn->scrnIndex, pScrn->options);
         }

         /* Done */
         return TRUE;
     }

20.3.10  SwitchMode

Define the SwitchMode() function if mode switching is supported by the
driver.

     static Bool
     ZZZSwitchMode(int scrnIndex, DisplayModePtr mode, int flags)
     {
         return ZZZModeInit(xf86Screens[scrnIndex], mode);
     }

20.3.11  AdjustFrame

Define the AdjustFrame() function if the driver supports this.

     static void
     ZZZAdjustFrame(int scrnIndex, int x, int y, int flags)
     {
         /* Adjust the viewport */
     }

20.3.12  EnterVT, LeaveVT

Define the EnterVT() and LeaveVT() functions.

These functions are mandatory.

     static Bool
     ZZZEnterVT(int scrnIndex, int flags)
     {
         ScrnInfoPtr pScrn = xf86Screens[scrnIndex];
         return ZZZModeInit(pScrn, pScrn->currentMode);
     }

     static void
     ZZZLeaveVT(int scrnIndex, int flags)
     {
         ScrnInfoPtr pScrn = xf86Screens[scrnIndex];
         ZZZRestore(pScrn);
     }

20.3.13  CloseScreen

Define the CloseScreen() function:

This function is mandatory.  Note that it unwraps the previously wrapped
pScreen->CloseScreen, and finishes by calling it.

     static Bool
     ZZZCloseScreen(int scrnIndex, ScreenPtr pScreen)
     {
         ScrnInfoPtr pScrn = xf86Screens[scrnIndex];
         ZZZRestore(pScrn);
         ZZZUnmapMem(pScrn);
         pScrn->vtSema = FALSE;
         pScreen->CloseScreen = ZZZPTR(pScrn)->CloseScreen;
         return (*pScreen->CloseScreen)(scrnIndex, pScreen);
     }

20.3.14  SaveScreen

Define the SaveScreen() function (the screen blanking function).  When using
the vgahw module, this will typically be:

This function is mandatory.

     static Bool
     ZZZSaveScreen(ScreenPtr pScreen, Bool unblank)
     {
         return vgaHWSaveScreen(pScreen, unblank);
     }

20.3.15  FreeScreen

Define the FreeScreen() function.  This function is optional.  It should be
defined if the ScrnInfoRec driverPrivate field is used so that it can be
freed when a screen is deleted by the common layer for reasons possibly
beyond the driver's control.  This function is not used in during normal
(error free) operation.  The per-generation data is freed by the Clos-
eScreen() function.

     static void
     ZZZFreeScreen(int scrnIndex, int flags)
     {
         /*
          * If the vgahw module is used vgaHWFreeHWRec() would be called
          * here.
          */
         ZZZFreeRec(xf86Screens[scrnIndex]);
     }

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$XFree86: xc/programs/Xserver/hw/xfree86/doc/DESIGN,v 1.13 1999/11/26 00:58:20 dawes Exp $